Resits, holidays, changing courses panic

Hi. Currently studying at York. I have a 3 week holiday booked and paid for. I'm going to see a relative who doesn't have long left to live, so its an important holiday for me. However, I have to resit my maths and get 60% to change course to what I want to do (computer science) since my A level maths result wasn't good enough. The resit period is bang in the middle of the holiday. Everything has already been paid for by my boyfriends family. I've asked if I can change resit date and they say no I cant. So my only options is to either take a 16 hour £1000 flight back 1 week into the holiday to resit, not go on holiday at all and resit, or go on holiday and change courses. I'm not even confident I'll get 60% on the exam. I'm panicking and don't know what to do. If I had to change course I'd go for interactive media but my mum slammed me and said that wont land me a good job and will be a waste of all my efforts to get to uni, and that by not trying to get into computer science with the resits i'll be a disappointment basically. I have no idea what to do if someone could help link me to resources or give me direction that would be greatly appreciated.