Hey, I don't think it should be an issue if you can find a college who'll take you. I moved schools for the start of y12, and we were allowed to move around subjects as much as we liked pretty much until November (so obviously people arriving at a subject late were expected to catch up on the work they'd missed). I also remember a new girl joining from China, who didn't speak English and had never taken any A levels - she joined around December I think?
I didn't enjoy it at that school, and ended up moving back to my old one about a week before the summer exams for both schools were about to take place. My situation's a little different to yours because I had already been studying my A level subjects for a year and was moving back to my other school which offered the same subjects. I fully expected them to make me repeat a year because my old school used a different Physics spec and also taught maths and further maths in a completely different order, but they just told me to learn the new material the best I could and see how I did on the exams. They decided not to make me repeat a year and I'm sitting my A levels in June now
So yeah, long story short, three months is nothing, even if those three months have been spent not doing A level subjects. You have plenty of time to catch up - if I could learn the whole of AS physics on a different spec in three days, I'm sure you can catch up on only three months of missed work in a year.
Just make sure you have another college lined up for you who are willing to take you on and invest the time to catch you up, and also make sure you are willing to put in the work to catch up on the material you've missed.