change of mind on signed contract 🙈

I know this is completely off topic for this app but I need advice. Can I change my mind after signing a change of contract? They have taken 5 hours off my contract and I'm struggling as it is. It won't begin until January 1 but the hours aren't suitable for me and I won't be able to get home as it is late night and I live about 5 miles from my work. Tia x