I got one of those packets where you just add milk and an egg.
I followed the directions precisely. The only thing I can think of is; I mixed the ingredients, then realized I hadn’t turned the oven on yet. So the mixture just sat there in the pie pan until the oven heated up to temp.
I also vaguely remember that you shouldn’t mix the batter too smooth. But I’m not sure if I’m remembering that right.
Pls, help. I’m making chili tonight! 
If the packet is old it’s possible the baking powder in the mix has gone stale. Beyond that I’m not sure, I tend to make it from scratch (which is super easy, btw) so I don’t know what else could go wrong with a packet mix.
This is also important. If you mix it to death, you can lose all leavening. That can also flatten out the mixed cake. Something I do is sieve the dry mix, then beat the egg and milk separately, then just stir wet and dry together. You can bake without preheating, that’s not so important. IMHO.
You shouldn’t skip preheating when using baking powder. Most baking powder is double-acting, that is, it activates in the presence of liquid and ALSO heat. That’s probably why it turned out flat.
Yep, you should have lumps.
I’ll be the party pooper and say that since it’s a mix, the entire batch at the factory might have omitted baking powder. If you still have the packet/box that the mix came in, contact the manufacturer and say, “Your cornbread is FLAT.”
You will probably score some free coupons.
~VOW
It was probably because you didn’t preheat your oven. Double-acting baking powder releases CO2 both when it is mixed with liquid and when it’s heated. This causes the cake to rise. The heat of the oven also causes the batter to set (i.e. become solid) when it gets hot enough. If you put the unbaked cornbread into a cold oven too much time can pass between when the gases are released and the batter sets. The gas escapes from the liquid, and you get a flat cornbread.
Looks like this has been answered but I can’t stop myself. Over mixing is your problem. Took me a long time to learn this. A few quick strokes, a few minutes to sit then into the oven.
Since your main question was answered let me suggest that you also heat the pan before everything goes in the oven. If you have cast iron that would be best since it will get hotter and stay hotter longer, but even if its just aluminum grease your pan and toss the pan in the oven while the oven is pre heating Then pour the batter into the hot pan. You get a better crust that way.
I can see where overmixing and not using a pre-heated oven would affect the degree to which the cornbread would rise.
My take of the OP’s problem, though, is that the cornbread turned out to be johnnycake. With absolutely NO rising whatsoever, that (to me, anyway) sounds like there is NO leavening in the mix.
~VOW
A general note about baking powder: It needs to be shaken before being used. You’ll find that instruction somewhere on the can, but most people don’t know that.
I can’t imagine that’s for anything other than to break up clumping. My Clabber Girl brand baking powder contains that instruction. My Kraft Calumet brand does not have any such instruction. I’ve never bothered and have never noticed any problems.
That will screw up your cornbread right there. Oven must be pre-heated.
I had a similar experience when I was making some cornbread for a party, and someone had turned off the oven, thinking they were doing me a favor. Didn’t realize it until the cornbread was in the oven, and then had to heat the oven up all over again with the cornbread sitting there.
It came out flat, just as you describe.
That’s what you get for using low-fructose corn syrup.
the batter not being linked and thickened by heat, then being unable to trap the gas, would have the same effect as the gas never being generated.
I use Martha White Sweet Cornbread mix.
At first I got these strange bumps on the top of my muffins. Like a pinky finger on one side, but shorter. One day I noticed the fine print. Beat the egg in a separate bowl and then dump into the batter. :smack: Made a huge difference. Cracking the egg directly into the batter results in the yolk and white not getting beat together correctly.
Add a bit more milk. My mix calls for 1/2 cup. I find that mine rise better with a little more. About half-way between the half and 2/3 cup mark on the measuring cup.
Finally, keep the mixer in the cupboard. 
Yes, years ago I foolishly beat my cornbread batter and it came out like crap. Now, I beat it for about 20 seconds with a fork and that’s all. Let it sit about 5 minutes and then pour into the muffin pans or cake pan. I personally prefer cornbread muffins.
Maybe they mean that user is supposed to shake, not the can. . .
Seriously, I had no idea people bought cornbread mix. It’s soooo easy to make from scratch, and then you have cornmeal around for stuff like dusting your pizza stone.
People buy mixes for everything. There was a thread some time ago where a dude bought a taco mix. Not a little packet of taco seasoning, but taco shells and seasonings and sauce all packaged together and then decided that ‘home cooking’ was no cheaper than eating out.
That being said, I overmix everything from muffins to pancake to cornbread batter and I make no apologies for it. I can’t stand seeing little lumps of flour floating in my batters and no one has ever accused my baking of being tough or flat.
Preheat the oven. Use a hot oven, 425F or above. Preheat the pan with corn oil in it. Use corn oil for shortening and to grease the pan that you preheated. Don’t overmix, it should be lumpy. Use coarse ground corn meal. Use buttermilk, and add baking soda, about 1/4 the amount of baking powder (in addition to the baking powder). Use molasses, or dark brown sugar. Don’t make more than you can eat at one sitting, because you’ll end up eating that also at the same sitting.