I'm gonna go ahead and disagree with a lot of posters and say don't do it.
I kinda went a similar route. I was a double major in a science and a language, and was about a class or two away from a minor in music. Don't get me wrong, I loved what I did. But it didn't do my gpa any favors, especially since I refused to slack on my extracurriculars (so I always had one or two jobs, various clubs, music stuff, etc). And while I graduated in 4 years, I still had to take some time off after college to a) breathe and b) try to get some research experience in cause I just hadn't had the time to do that properly. So I honestly wish that I had stuck with just the language and the music cause they were the subjects that made me the happiest and that I ended up doing best in. The hard sciences do not serve themselves well to being somewhere in the middle of your to-do list- they tend to take up most of your time. Unfortunately, because of my other zillion commitments, something had to give and a lot of the time that turned out to be acing my science classes (and my sanity and sleep patterns).
So my advice is to study what you love and what you know will help your gpa the most. If it's psych, go for it. Get your A's, take your premed pre-reqs, learn a new language on the side if you have time. That way, you won't need a backup plan (does a biophysics degree really guarantee a job in this economy? Cause bio/neuroscience/biochem majors are useless right now, I dont see why biophysics should be so different but I don't know much about it). On the other hand, if your passion lies in biophysics, then maybe take one psych class along with a few pre-reqs and biophys classes to see how you handle the workload, then add some EC's, then slowly try to incorporate all these things and see if you can do them all. Just don't overload in the beginning.