Hey there!
I totally get where you're coming from, I'm currently studying biomedical science in my 3rd year and was faced with a similar dilemma when applying to university.
Psychology can be competitive, especially if you're thinking of postgraduate study after your degree. However, if you're genuinely passionate about it, that enthusiasm can give you a boost and keep you resilient when facing setbacks. You'll have all sorts of career paths to choose from, and if you're really passionate about a particular area, you'll most likely have the option of going into postgraduate study to specialise in it.
Biomedical science can be a real battleground, if you want to become a biomedical scientist you will need to study an IBMS accredited degree and complete your IBMS registration portfolio in an accredited laboratory to register with the HCPC, that is providing your course is not already HCPC accredited like the Healthcare Science (Life Science) course. Placements are scarce and usually given to Healthcare Science (Life Science) students as they have a guaranteed placement. It's no walk in the park, but determination can get you there. Specialising in physiology as a biomedical scientist offers a wide range of career possibilities. You might discover yourself involved in research, contributing to healthcare, exploring the pharmaceutical sector, or even embarking on a path in academia.
Think about what you're passionate about and where you see yourself in the long run. Are you more inclined toward research, patient care, or academia? Writing an intertwined personal statement for both psychology and biomedical science is a valid approach, especially if you find it challenging to make a definitive choice at this stage.
Wishing you the best of luck with your choices and studies!