How can I get my phone to boot again? I have a Samsung Galaxy Mini (GT-S5570) and the ROM I'm using is CM10.1, I was messing with the developer options and I saw an option called "simulate second screen" and I  clicked that and selected 720 then it froze. I rebooted it and stops at the end of the boot animation and get stuck there.

Any ideas please?
Did you try "Volume Up + Menu Button + Power Button"? 
That should get you to Recovery Mode and you should have an option there to Factory Reset your phone.