I don't think you will get very far in this effort to get paid, unfortunately. At best, you might get the latest deposit refunded, but not the previous ones.
If SIA did transfers with other books ( they don't, which is a sign of a bad book) you could leave the money there until you were 18, then transfer to another book.
In your case, ( you want the winnings, not just the deposit), a trusted friend over 18 with an SIA account that you could dump chips to in poker is probably the only option. I can't think of any other way. Even if you waited until you were 18, you might not get paid, if they investigate the account.
You pretty much screw yourself by playing underage.... you can deposit, but hard to collect. The books have a responsibility to prevent underage gambling, not being able to get paid is a pretty good method to deter those that are underage.
Why would parents find out, unless deposit came from their money ?
You are pretty much screwed here, but it is your own fault.
I'm sure you could get paid by some books ( I won't list them), but SIA is well known for requiring documentation before eventually paying.
Poker is your only shot, IMO ! You need to play head to head with your buddy, and have him on the telephone.