Argh! Help! Parents!

Ok, I've been building a fixie and it's finally finished and at the shop waiting for the unbelievable labour cost to be paidfor it being put together, and i get home from school and my mum says to me, "Alex, you can't ride you new bike, it's too dangerous." And I'm thinking to my self: WHAT THE FUCK IS GOING ON?!?!?!?
So after a bit of arguing she says she thinks its to dangerous, and we'll have a talk this evening when my dad gets back.
I'm 15, its got a front brake on it and I'm running on 41tx18t.
I need help persuading them to let me ride.
Any one got any advice?

My daughters are a little older than you (17 and 18). If they were riding 41x18 I would tell them to HTFU.