Evaluate what the consequences of getting a 90% average are, and decide whether it's going to hurt you or not. If you're applying to very selective schools it likely will. If you're starting your own company it won't matter at all. I did most of my work during my lunch period (it's astonishing how much busywork you can bullshit your way through in 30 minutes--I almost never had any work to do at home except for AP classes), ended up with a mid-90s average, got into a very good college, and am very happy with how things turned out.
Don't ignore the things that don't interest you just because they don't interest you. Even the things that aren't directly relevant to your future can become very useful in unexpected ways. School might be an incredibly inefficient way of learning things for you, but if you're forced to be there, put the time to good use. (I might be very happy with how things have turned out in general, but I do wish I'd put actual effort into my foreign language classes.)
One thing to look into is graduating early. I graduated a year early from HS, and it's one of the best decisions I've ever made. (I'm now a senior in college.) I had to take English classes at a local community college for one summer to satisfy requirements, but otherwise it didn't really change much for me. If you're interested, talk to your guidance counselor now. I started planning in the beginning of my sophomore year.
I should really be doing work right now, but if you have questions about anything or would like someone who's been through this before to talk to, my email's in my profile.