My question to you is, why not? Second, you must go to the subject that you like most or have an interest in, and for this, the very best option I can give you is to help you discover your needs and real choices. Go to Google and read about HRM, Psychology, and their scope.
If you want to know from others which subject you should choose, there are lots of suggestions. However, I recommend that you go with HRM, which is expected and obvious as it is the field for HR professionals. You should visit
https://www.citehr.com/16473-psychology-hr.html, and I am sure this will certainly help you make your decision.
You can also refer to the following discussions where members have already talked about this same topic and have defined how both HRM and Psychology are connected to each other:
https://www.citehr.com/114784-hr-psychology.html.
Based on my personal and professional opinion, I suggest you go with HRM.
Thank you.