pine can be very tricky. As for trying to "fix" them - not too easy. You could primer and paint and forget about the stain though. If you really need to have them stained then perhaps try rubbing the dark areas with paint thinner on rags and maybe try using more or darker stain on the light parts. I wouldn't hold out much luck for you and I wouldn't try it myself. If you want to start over then bring the door to a real woodshop, where they can run the door through a big sander to start fresh.
Pine staining: I always use minwax brand "wood conditioner". Helps prevent blotchies. Follow directions. You have to use slightly darker stain to get same shade when using conditioner. Also, the way you sanded it might have caused blotches. All areas of the pine needs to be sanded exactly the same and start with about an 80 grit and end with a 100 or 150.