11’s are a chore to play if you are just starting out and used to 9’s, say. I would get the strings changed back. Bottom line - if it played well set up a certain way and now it does not play as well, something changed. If you basically liked the guitar before, try going back to a lighter gauged set…
Otherwise, the posts in this thread are covering string-changing basics. I would totally take off that trem cover from the back of your Strat - I never had much use for the covers and having it off eliminates that “lining up” problem. Just stash it in your case with the screws in a little plastic bag so if you ever sell it, you have all the original parts…
I think **River Hippie **or someone else recommended the Strat book - but it is a good one.