I think the best thing for you to do is contact UCAS tomorrow and request for your place to be withdrawn. You should explain the situation to them, make sure you have done your research today on any areas that you do have an interest in and make a list so you can go through clearing tomorrow. I'm not sure if it's definitely possible at this stage to do that, but it's worth a try if you really don't want to study the subject anymore. Is the course that you want to do related to biomedical science in any way, or is it completely different? I hope that helps.