The SPECWAR billets are few and extremely competitive at the Academy. Major is less important than order of merit and physical fitness. One of my company mates was a PT animal but didn't get picked up for NSW because of his mediocre grades. The competitive Mid will be on the Supe's List, excel during Mini-BUD/S (and it's tough getting selected even for that), go out for Jump and Dive schools and excel (you essentially try out for Jump and Dive if you want to go, though even if you pass you may not go due to budgets/billets...Mids get to go when absolutely everyone in the Fleet has had first refusal).
Wanting to go into NSW is a great goal. Just calibrate your expectations accordingly. You're going to school with a lot of very fit, scary smart, ambitious and driven peers who want to be SEALs just as much as you do.
There's something like a dozen Specwar billets each year, for an Academy class of about 1300. An alternative possibility is going into another community on graduation and applying for lat transfer after a couple of years. I knew a few guys who went that route and successfully made it to the Teams.