You can switch programs, however, I would suggest focusing on getting a Psych degree. Generally, grad schools want you to have an Hons. degree, which means more courses. Even a 3 yr BA is going to need additional courses since there is a minimum that you need. If you decide only to pursue the bio degree and try to get into I/O you will need to take the Psych GRE and score in the top 80-95% to show you have understanding of the field without getting a degree in it.
Some university programs also only look at your last 60 credit hours (2 full-time years). If you applied this fall, they would look at your year 2 and year 3 gpa. They do not specifically look at psych courses, though they may consider how you did in them compared to the bio courses when you give an explanation in you letter of intent as to why you changed your direction. Most graduate programs require a minimum of 3.0 on a 4.0 or a 4.5 gpa scale. I would strongly suggest spending the extra time getting the psych degree (you likely have the rest of your requirements, expect maybe an extra humanities courses outside of psychology) so get the courses under your belt, do up a thesis, and see if a high level stats course will be comparable to the psych stats (senior level), this might save you from having to take a heavy extra course. The other thing is to get some research work, with a prof or otherwise, to show your interest in psych research. Good marks in psych, though! This is doable, it just make take more than a year to get there. You are not the only one that changes their mind over their program, I knew one guy with A/A+ in 20 credit hours per semester, took 8 years and still finally walked out with a degree. He could have had six different degrees, but always changed his mind before taking the last required course. Extreme, yes, but in comparison, you are sitting in a possible situation. Best of luck!