I never did bio at school, but did it last year as part of a science degree, and the first probably 4 weeks or so I struggled to understand what the hell they were talking about (like, seriously, I didn't even know what a prokaryote was, lol) but once I got my head around the language, I was fine. Just be willing to put in the work, it will probably take you 3 times as long to read one page of the textbook, coz you're constantly looking things up, but once you get your basic knowledge down, you'll be fine.
In the end, bio was my fave subject and I did well in it!