Doubling up on science classes is definitely not a bad thing if you can handle the workload. Sometimes you will see crossover in concepts that will help you. Keep in mind that science courses have intensive study demands (especially organic chemistry), so make sure that those demands fit in your schedule and if you feel that the load is too much once courses begin, drop the extra biology class BEFORE the withdrawal deadline. As an estimate, I would see if I could commit to at least three hours/course per week of study time.
For context, I doubled up on STEM courses almost every semester and had to be very intentional to pick the rest of my classes around those courses as to not be too overwhelmed.