Basically speaking, biomedical engineers need to have additional knowledge and eventual expertise in biology, biochemistry and physiology. It helps to know computers -- as with all engineers -- but also electronics. Biomedical engineers are essentially mechanical engineers with additional knowledge of the human body. I assume you're only talking about human biomedicine. The thing I would recommend is to contact a counselor at a school that produces biomedical engineers and ask for a required course list. This will give you excellent insight into the different requirements. I would also, as usual, seek out biomedical engineers who are currently working and ask. This is a pretty logical step that many students simply don't try. Now, as with all engineers, you'll find quite a range of actual activities and projects. Just as medicine branches out wildly in terms of specialties, engineering does as well. I personally have been extremely fortunate to have worked on a wide range of projects, and this has given me a lot of very enjoyable experience. However, that is not the rule. Some engineers have focused on one particular job or specialty. So I would recommend talking to as many people as you can find to give you advice. You'll also find this pretty enjoyable.
In my university, Biomedical engineering was split into three: Biomechanics, Bioelectrical and Biocomputing. So you can go a lot deeper into any of these topics. If you don’t want to limit your knowledge to just the medical field and devices, then you can explore a little more with Mechanical engineering.
Mechanical engineers concentrate more on product manufacturing and fixing technical issues while biomedical engineers can concentrate on a number of specialization areas that may emphasize medical research or developing methods to diagnose and treat medical conditions.
Mechanical engineers are a little more broad in focus, anything having to do with mechanics. Biomedical engineers focus more on any engineering that has to do with biomed. So a mechanical engineer could do biomedical, but they may need some more specialized training with the medical side of things to excel. Basically they're very similar, biomeds just have more specific training in a more specific field.