People pleasers or previous people pleasers: I need advice

I have generalized anxiety and social anxiety. Ever since I was a kid I have always wanted to keep the peace, not rock the boat, not upset anyone. Is it the anxiety, or my parents consonant fighting who made me this way? Did the anxiety come from my parents or my parents made my present anxiety worse? The chicken or the egg? Who knows. Anyway up until a few years ago I had a hard time disagreeing with people. My whole life I’ve been called “nice”, never knowing if I am actually nice or I was just agreeable to not cause issues/for people to like me.

Now I’ve been trying to be more open about my opinions, instead of pushing things down and getting upset or irritable. However there are times I still feel like an asshole. For example today I was out with my mom shopping. She picked out a dress she said was cute, and asked if I’d want it. I said no, it wouldn’t fit me right and the top and bottom portions didn’t match. Usually I would have gone as far as trying it on, saying I liked it, and letting her buy it for me before saying no. Was what I said ok, or too harsh? Another instance is TV shows people suggest. I’ve had friends suggest romcoms to me, when I don’t like romcoms at all. I always would say I’ll check it out, and I never do. Now I’m trying to be more open about my preferences (while trying to not put down others preferences). Should I just say “yeah I’ll check it out”? How do I get past this uncertainty of the right and wrong thing to say? Thanks.