Can I change my GCSE subject?

Ok so I just started school (Year 10) last Wednesday (6th September). In year 9 we chose our GCSE options. I chose Geography, Computer Science, Business Studies and Film Studies (btw they r going in order from 1-4) My school told me repeated times that you are less likely to get your last option so that is why I put film studies as my 4th choice. I ended up getting Geography, History and German(which I am okay with) and last but not least Film studies. They couldn't even give me Computer Science or Business Studies which were my 2nd and 3rd choice. I thought to myself I just need to suck it up and do it for my GCSEs. So now being in year 10, I have had 3 lessons of Film Studies and I hate it. I really want to change to Computer science because I can't change to Business Studies( the classes are all full) but I don't know if my school will let me. I really cant carry on doing Film Studies, it's just not for me. I made a mistake choosing it for my options. I just found out that Film Studies and Computer science lessons run at the same time so hopefully there is a bigger chance that I can change subjects. What do you guys think? Pls help