Toddler gymnastics

My 3 year old daughter completed her gymnastics intro classes and starts her regular classes on Monday. What should I have her wearing? Is it okay to keep her in athletic shorts and tank tops for the classes or should I get her some leotards?

I posted on here when my husband and I first signed her up. Since then she has had two 25 minute intro classes. Her attention would drift a bit at times but she did show some improvement from one week to the next. Starting Monday she will have hour long classes in a group of 8. Anyone with kids in gymnastics, did your kid's attention improve?

Any other general advice is also appreciated as well.