So much of it is genetics and hormones, really, truly. So don’t feel bad if you never have a really flat belly. Outside of where your body likes to store your fat, abs are much more about your diet than exercise, and you’re on the right track there.
My belly is relatively flat and has good muscle tone and definition, but it comes pretty naturally cause I’m a lean pear shape like the rest of my family. I still have that little ‘pooch’ around my navel though, and I’m really skinny. As I continue to gain weight I will only have more curvature there. Like my fat butt, just part of being a woman. Having barely any breasts is also part of being a woman, for me. 
I don’t do any targeted ab exercises. I do exercises like planks, head stands, hand stands, many types of squats, and deadlifts, that create functional core strength.