just go ahead and apply for a personal loan for $500 with your bank, it does not require credit pull
Whew, good! Also, what you should note is that the car loan will report for a while as a positive tradeline even though it's PIF, so you don't NEED another installment loan. Take your lender's advice adn don't open more credit. Your balances are really the key to the credit score you want. Work with your lender closely so you don't overspend money that should be used for reserves/down payment and good luck!