There are many accountancy specialisms you can explore. If you’re unsure, try applying for a smaller/mid-tier accountancy firm role as you’ll get exposure to different areas early on compared to applying to a big 4 firm where you’ll be asked to choose a specialism from the outset.
As for going for a masters, it really depends on what your rationale is. If it’s to improve your undergraduate grade then it makes sense to do so. Otherwise, doing a professional qualification makes more sense if you’re certain about going into an accountancy role. Employers tend to pay for these qualifications.