You're going to have to see if you and the person whose car you damaged can agree on a payment plan;  if possible, you should look into borrowing the money to pay the person, and then pay off the loan.

It was the right thing to do.  I hope the person you're dealing with gives you some credit with that, and I hope you have good luck finding that loan.  If more people were as honorable as you, there'd be a lot less work for us lawyers.