If I understood the question properly, you knew that things have been stolen from lockers, yet kept the money there anyhow. That seems very irresponsible to me. Probably, al pi halachah, you would be responsible even if that wasn’t the case, since you left it in an unlocked place.
So, the way I see it, you have to find a way to earn $50 to pay back. Do you babysit? Do you have Chanukah gelt or other money?
You might want to ask a shailah if you are indeed obligated, but keep in mind that your friends probably wouldn’t be too thrilled if you don’t make good, even if technically you didn’t have to.
As far as the grammar and spelling, please keep in mind that sometimes not proofreading your posts can make parts of them incomprehensible.