Hi, I'm in the advanced level and have chosen biology as my advanced level. I'm very unsure about my decision. How can I give myself hope?

As described above, I chose advanced biology. Of course, I thought about it and didn't choose it rashly. But now I'm terrified of what's coming and that I won't be able to do it. I'm also very scared of biochemistry and the tasks involving operators. In general, I tend to panic whenever I think about it.
Can you give me some hope? And give me tips on how to best master the subject? I was considering switching to physics, but it's too late for that now.