Can I study Occupational Therapy with these A-levels?

Check a range of uni requirements and see if you meet the GCSE grade requirements and a level subject requirements.
You can add the stuff about volunteering and work experience to your personal statement

Originally I wanted to study Maths, Biology and Chemistry. But my GCSES are not high enough, I'm only able to study Biology for A-level.

I didn't choose either Psychology or Sociology for my A-level as I haven't studied them for GCSES and I only studied Sociology for a short time in Year 9; I believe I will definitely struggle from them for my A-levels.

I studied Film and Media for A-levels as I would like to study Film as a back up.

I understand your concern and the disadvantages of my A-level subject decisions. I'm currently looking through the requirements for OT and maybe work experience to be able to compete with the others who study STEM subjects with Social Science and wishes to study OT.

You should be fine applying for most OT courses with one science A level (use the NHS course finder to check entry requirements for approved courses you would consider applying for).
Unis will want to see that you have some shadowing experience with an OT to show that you understand the job. Contact your local hospitals/outpatient clinics and ask for a day or two of shadowing experience (requests for short periods of shadowing experience are usually better received than requests for longer periods of work experience). Unis also want to see that you have public-facing work/volunteering experience to show that you are comfortable dealing with the general public. This doesn't have to be in a care setting so working in a supermarket or cafe, or volunteering in a charity shop would be fine. Consider volunteering in a care home in the summer holidays as this might also expose you to OTs visiting some residents to help them after illness or injury.