My bag looks like this (minus the big side pockets) http://www.bagsdirect.com/images/Products/Wenger%20Swiss%20Gear/hires/ga7306-06-back-pack-bag-shoulder-laptop-wenger.jpg and I want to use it on my trip to England so I can fit some of my electronics and my macbook pro in one bag rather than taking 2 carry-ons. Could I do that or is this bag way too big? I'm flying on American airlines if that helps anything...

Absolutely. The size is fine. When you get to the airport, I think you will find at least a third of the passengers will have some kind of backpack as a carry on item.

No problems.