Yes, why not. You can easily pursue M.Sc Psychology after your B.Sc nursing. yes You can go for M.Sc in psychology after completing your B.Sc nursing. You just have to fulfill their basic eligibility criteria as per the Institutes demands eligibility criteria for M.Sc in psychology is that you should have an undergraduate degree from recognized college. So you are eligible to do this.
I would suggest you to choose Clinical Psychology.
All the best!!