NO!!!! It doesn't matter!!!!
Personally, I would choose pyschology since I find it more interesting - as for molecular biology, taking the required one course, imo, should suffice for your interests. Unless you find molec bio that interesting that you would want to take courses beyond the introductory level, I would choose psyc...but only you know what you are interested in!!!
I find that, if you are majoring in a science program already, many of the advanced topics within molecular bio pops up in various courses anyway.