[abigailthefox]

Absolutely get more mentors. It's a hard job to take, but find dedicated parents/teachers, etc.
I saw this earlier in the thread, but if your school is willing to offer to pay your lead mentor(s) the same money they pay sports coaches, that should definitely incentivize it.
Also, (and I know this is probably against school policy, insert disclaimer here) we've had students in the past, typically seniors, stay and work without a mentor. I'm not saying you should do this, but if it's a few days before bag and you're desperate...
You should always have someone 18+ around, as well as someone who understands safety procedures for all tools/equipment. I'm assuming your team captain has access to emergency contact information (if they don't, they should anyways), and if you have that around, you should be good.
By all means, recruiting mentors is your best bet, try reaching out to engineers/software people in your community, chances are if they have a genuine interest in these things (even if it's not their day job), they'll be more likely to want to help, and potentially even willing to put in the long, grueling hours.