Has your sponsor given you a dress code to follow?
What one friend says is to dress for lunch at a country club.
Knee length shorts and capris are acceptable for lunch, but not for dinner.
Sleeveless blouses are usually ok. Tank tops are not. Running shoes should be fine.
What many do is pack the outfit they wish to wear, leave it in a locker, and change just before going to the club.
This was my 15 and 12 yo nieces last night for dinner.
Here is from when my kids were teens at lunch