Honestly, as a freshmen you need to pick a major that is relevant to your career goals or has some actual value if you were to graduate with it and not go directly to graduate school (seriously, trust me on this....My buddy is graduating in history with no plan at ALL because halfway through he decided he didn't want professional school). Be smart. Make the balance of practicality and interest with your degree. Then, I recommend nailing those prerequisites HARD and getting your A's. Many chems and bios are weed out classes. Make sure to balance your life as you adjust your first year. I wouldn't freak out about observation hours too much yet. Otherwise, you may be trying to observe too much when you should be studying. Balance is key freshmen year. Undergrad is a solid 3 years before applying (4 if youre me). If you have great grades, you can begin hitting your summers hard with observation hours in different settings with minimal if any classes to take. Then, you can start adding a shift or two during the year.
Also, if you print out ptcas forms now, then you can have pts sign them after observation I found out. Then, when you apply you can do electronic signature or paper based where you print out a new form and attach it to the signed form. You mail both in to ptcas. It's basically a safety net in case you can't get ahold of someone down the road.