You may need to rotate the jack so that it fits better. If you put a jack plug in the socket first, then it's as expanded as it ever needs to be. But loosen the nut on the socket and turn it round and there should be a position where it fits in juts fine, Happens on Fenders too. Just watch out for the tip connection touching any shielding you add at a later date.

Maple boards have a wide variety of options. Clear or tinted lacquer is the classic way, though people have used wax and various oils. If you leave it bare it will get dirty very quickly.