Paying cash for asset after discharge

What is the name of your state? - California

My husband and I were discharged about a week ago - CH7.
We did not reaffirm our cars and planned to make payments until paid off. However, we discovered the blue book value versus what we owe causes us to be upside down on both cars 50-60%. We found a used car for $7,000 and $3,000. We want to return our cars in BK and pay cash for the two used cars. Are we doing anything that will cause problems with our BK?

Thanks.