strongly disagree that studying openings is necessary to "do your best" at competitions. In my experience almost all games between players under 2000 (class players) are decided tactically. I'm expertish (2200+ bullet, 2200+ blitz, 1900+ USCF, win most local tournaments in my area etc) and I don't bother studying openings. Chess is 99.9% tactics at the class level. You won't reach GM without opening theory memorization but you wont reach GM anyway.

Also a reminder for anyone reading these comments that chess should be fun! Don't let psychological hangups like thinking u need a good memory, thinking you need to study openings, have a certain level of skill, or need to play a certain format (like avoiding blitz because it is "bad" for your game or thinking OTB is more important) stop you from playing chess! The only rules for how to play chess are the rules of the game; all the other stuff e.g advice about how to get good are just things people make up. Learn and play however you want and in whatever way brings you the most joy! Chess is a game and it is meant to be fun and not be taken seriously

I think I'm just salty (and overfitting) that my cousin studied one opening to a stupid depth and beat me ~10 games in a row with it

That echoes my experience as a much weaker player as well. I improved leaps and bounds by studying puzzles. Not so much by memorizing openings.