Unsure of how to go on

I attend a school in the uk, just finished secondary school and didn't get the grade the grade I needed, I got 55 in combined science and I wish to do biology. (I know my biology grade is much higher as I usually get grade 6/8's). This is where my dilemma lies, not sure if schools would accept me but I know my current secondary school would as they are quite lenient. But unfortunately they don't offer computer science (which is my first choice A-level and I desperately need it as it will be important for my career path). My secondary school only offers IT as an level and im not sure what to do as I wish to study in Cambridge in the future .
Also, I wish to have a degree in computer science so that I can become a software developer, and if that didn't work out then some type of doctor. Any advice?

not sure if schools would accept me but I know my current secondary school would as they are quite lenient.
You need to ask the individual college/school. No one here can tell you for sure.
they don't offer computer science (which is my first choice A-level and I desperately need it as it will be important for my career path)
You don't need a degree in computer science to become a software developer. In fact, if you know how to program and build your own software, you're already there.
If you want, you can go straight into an apprenticeship in software development straight after A Level.
If you are a master programmer with skills rival of that of even the best programmers out there, companies can hire you as you are now; no further qualifications required.
If you want to do a degree in computer science, the more important A Level subject is Maths, not Computer Science. Check the entry requirements of each individual degree yourself.
My secondary school only offers IT as an level and im not sure what to do as I wish to study in Cambridge in the future .
Where you say Cambridge, which uni do you mean? Cambridge has 2 universities: University of Cambridge and Anglia Ruskin.
I wish to have a degree in computer science so that I can become a software developer, and if that didn't work out then some type of doctor. Any advice?
Getting into a degree in medicine is significantly more difficult than getting onto a computer science degree.
A degree in medicine generally has higher grade requirements, have stricter requirements, involve interviews, highly competitive, UCAT/BMAT aptitude test, fitness to practice statements, a personal statement second to none, relevant work experience, squeaky clean criminal record, and have more specific subject requirements at A Level.
Most degrees in computer science would ask for Maths, Physics, or Computer Science as a required subject. Some don't even require specific A Level subjects.
Most degrees in medicine would ask for at least Biology, Chemistry, or both. Typically, you would need at least straight As, and even then there's no guarantee you would get in.
If you're not absolutely serious about medicine and consider it the only thing that you would ever want to do, I wouldn't entertain the idea of becoming a medical doctor; it's a lot of hard work, a lot of years of your life, and a very stressful environment. It's definitely should not be considered as a back up career option.