The thing about playing any sport in college is that it is a full time job. I hope your parents are generous and understanding. Most college kids can hold down 2-3 jobs and bust their butts in the summer, you can't. Summer will hopefully be playing with a summer league and winter you will likely be taking courses to make up the light load of credit you take during the fall and spring so you can keep up with baseball. 12 credits is a "full time student", but 12 credits won't allow you to graduate in 4 years.
As for college itself, it was eye opening to many. Who the heck is going to wake you up for these 6am workouts?
Hope you don't think it is odd to study for a test on Tuesday that you don't have until Friday, because you only have a free block open on Tuesday! What many athletes did was write up note cards with blanks, answers on back, on Tuesday and then study just those note cards on Thursday night. You will become an expert at time management.
With D3 you can run the gambit on the talent level. I've seen a D3 team whoop on a low D1 team. I've seen D3 players get drafted, all you can do is worry about YOU! Do your best, make your grades your number 1 priority, support your team and teammates the best you can and hopefully the rest will fall into place.