That's a fairly common break point on a Nexstar. I broke mine in just about the same spot when I was learning to fly. The repair was fairly easy and we (my instructor and I) were flying the next weekend.

One thing. You said you were using the instructor's plane in your original post. Perhaps I read it wrong, perhaps you meant that you used it only on your solo flight. But, if you had been using the instructors plane all week, perhaps it would have been best to fly the Nexstar with the buddy box before attempting to solo. If you had been flying it all week, then I stand corrected.

I highly recommend our student flyers that they buddy box with an instructor for the first few flights for their second plane or any time they may feel that they need a little help with a new 'design' or something that is totally different from what they had been flying in the past, such as going from a high-wing trainer to a low wing second plane. That's just a suggestion and not meant to be critical by any means.

Congrats on your solo. I know how it feels, believe me. And it always feels great as an instructor when a student solo's.