If I were you and had it to do all over again, I would stick to a degree that is non-aviation related, preferably business or accounting or something that would help you as a side job while flying the line. As far as grades, no one really cares as long as you graduate with a degree. Most prospective employers will ask for college transcripts but thats usually just to verify that you did, in fact, do the things you said you did in college and graduated with the degree you said you have.

You're young and your path need not be the shortest, straightest path from Cessna 152 to A380 captain. There are lots of rewarding and interesting ways to make a living flying airplanes and the journey is half the fun. It also makes you a far better aviator (and more fun to have a beer with on overnights than someone who only knows airline flying. When you're with a crew, we all know what being an airline pilot is like. No need to discuss further except maybe a few war stories or funny things that happened to you in airplanes. Beyond that, the guys I like flying with the most are the ones that share common interests OUTSIDE of the cockpit like cars, boats, business, girls, whatever. All the things that most airline pilots think about besides flying airplanes Even the ones that we share completely different interests or views on a topic can be great and I have wasted many otherwise dull hours criss-crossing the country engaged in good spirited, lively debate about something.

I would suggest you start plugging away at your pilot ratings (private, instrument, commercial, multi-engine, etc) while in college. Go out to a few of the flight schools in your local area and talk to instructors and other pilots out there. You'll find that most local airports are little communities in and of themselves and you can learn a lot just by talking to instructors and other pilots. Make sure you check out at least a few places and find one that can meet your needs and where you feel good about the people.

Speaking as a former instructor at both a small-medium sized FBO and a large university flight program (UND), the one single best tip I can give you is MAKE SURE YOU HAVE THE MONEY IN LINE BEFORE YOU START TRAINING. I can not tell you how often money is the single biggest obstacle to a student's training. It happened to me before I got smart about my training and I saw it happen to countless students. I'm not saying go into massive debt in order to finance your flight training, just make sure you have a plan to pay for it so that the pace of your training is effective for learning. When you are trying to learn a new, complex skill, repetition is key and long breaks while you are trying to scrounge up money to fly are a huge detriment and will end up costing you more money in the long run in the form of review and the length of time it will take to master each new maneuver or skill.

Hope this all helps. If you have any specific questions, feel free to PM me.