Need help with minor contract cross-state urgent

I'm a minor and am kind of in a bind. I was sent 6,000$ to build four computers (3 processing computers and a server) and send them to someone in California. I reside in PA. The money sent to me was used to build the computers with a 300$ profit. I built the computers, and sent them to him. I video proof that the computers worked before I sent them. I shipped them through a mailboxing store on my street, and they sent it through FedEx. I insured them for the full amount.

He received all 4 of the computers broken, now hes demanding a refund. FedEx is denying any insurance claim currently for inadequate packaging (in my defense, I used the same packaging that the computer cases were shipped to me in). Since I used his money to build the computers he is coming after me for 6000$. What should I do? Is this contract voidable? I sold it to him through a website, does that matter?

I didn't do anything wrong.. and have been more than helpful and supportive to him. But he is a very threatening and demanding person and wants to take me to court. If FedEx does not pay the insurance is he going to go after my parents?