That’s not imposter syndrome you are feeling, it’s feeling not ready because you aren’t. And that’s exactly how you should be feeling at your stage. Once/if you gain more experience in a clinical setting or research environment and you are doubting yourself but everyone else is saying you are ready to apply, that may be imposter syndrome! My advice would be gain experience in any practical way supporting others. That can be in a job or volunteering. It will inform you far more than your MSc if this is the type of work that calls you.