I was having the exact same problem! Clinical psychology is the most competitive job however there are alternatives such as Forensic Psychology (working with criminals to assess their mental state etc. you get the benefit of working with mentally ill people and helping them) so you should google it! There's many branches: clinical, counselling, educational, forensic, health, occupational, sports and teaching/research.
The main problem with mental health nursing is not only does it limit your chances whilst on the degree (placements are time consuming, you're in self-catered flat with other nursing/midwife applicants, if you don't like it you're stuck unless you drop out, limited social life) and after the degree as you're only qualified for mental health nursing, no other branches of nursing and means you'd have to go back to university in some cases if you wanted to change career paths.
On the other hand, psychology degrees are beneficial for almost every job, you can enter into different branches of psychology and different specialties OR another career path and a degree will make you more appealing, you have many many more opportunities with a psychology degree.