How to cover?Please help!

I have these scars on the top part of my thigh and I am going swimming this weekend with my friend...problem is were going swimming at a lake house with her family and no one knows what I have done...the scaring happened in the past and i am getting help but she doesn't know anything about them and it happened in the time gap from last summer to this summer and I don't know what to do or how to cover them or how to make up a story(and I know I shouldn't make up a story but her family is really judgy and I don't want to explain it plus it happened a long time ago)I don't know what to do. Please help!!Any advice?