Having a 2.75-3.0 isn't the end of the world, That's a B/B- average. It probably won't rule any field out for you, but it certainly won't help when if you apply for a competitive field. If you do, the rest of your CV better be stellar. Chances are it won't matter much at all for the less competitive fields.
Having a 2.1 on the other hand looks much worse. That'll likely put you in the bottom 10% of your class and basically kill your chances in most competitive fields (unless you make some really strong connections) and can hurt your ability to match into strong residency programs in less competitive fields. If you do well in clinical years (3 and 4) then many places won't care as much about your pre-clinical mistakes, especially if a place you rotate through loves you. Keep in mind that there is much more to it than just class rank/GPA. Board scores, preceptor letters, clinical grades, and interviews typically play a bigger role in where you can match than your class rank. Not saying it doesn't matter, just saying it's not everything.
Also, they can pretty much do whatever they want from residency onward. Once you're a resident literally nothing from med school matters other than research and connections you've made. Just like nothing from pre-med matters in med school and nothing from high school matters in undergrad.