What do I do now?

<p>Okay, so here's the thing. From the beginning of my A levels, my parents pushed me towards studying engineering and I applied to all my colleges for mechanical. I currently have offers from Imperial, UCL, Bath, Sheffield, Cardiff in England and Mcgill in Canada. I've always wanted to study math and have finally convinced my parents.
I had AAAABBBB in my O levels which isn't great and I'm surprised Imperial even offered me a place. I need A*AA in Math, Physics, Economics to meet the offer.
What I wish I could do is to get the grades and ask them if they can transfer me to the math department which I don't know is even possible. Imperial requires an A in further math which I don't have.
I've heard that inter faculty transfers are relatively easier at Mcgill but I wouldn't know for sure until I get there. Can someone help me with that?
Also, what do you think of taking a gap year after my A levels, taking further math, sitting for the SATs and trying my luck again at English universities and a few American colleges?
Or should I just settle for Mcgill and transfer to math?
I understand I've been an idiot and it's a stupid time to change EVERYTHING but I don't want to be miserable doing what I'm not interested in.</p>