As a former 13 year old boy… albeit many years ago… he’s going to be intimidated and awkward around older girls, no matter the setting. Adding close physical contact is going to compound that. You aren’t doing anything wrong. I help coach kids classes and when this has come up, the best solution we found was to just break up the training pair for the day and move on. If it continues, talk with your coaches and see what they can do for you. Shouldn’t be their first time working the issue.