I'm doing really badly with practice questions. Will I ever improve?

YES. Oh goodness, yes! Just stay determined and work hard at practicing as many questions as possible. There are lots of resources out there and I really recommend that you just work your way through every single question. I was so worried that my lack of maths A-level would prevent me from succeeding but I worked really hard and it paid off. I recommend the 1000 UKCAT practice questions book - I even took it on holiday with me that summer!