YOu can get away with not sheeting the wing. However I would take some of the advice given and sheet back to the main Spar and then drop on the T.E. and sheet about 2" back there. Plus I would sheet the middle. As far as looking good or not, that is a matter of opinion. Sheeting the whole wing on a trainer is something that I wouldnt do. There is NO need in it besides adding weight.
Plus the sheeting on the center is NOT the same as the sheeting on the rest of the wing. They both serve the purpose of strength but with proper wing construction you can get away with not sheeting the outer part of the wing where the middle sheeting is used for a different kind of strength. The middle is where the wing generally attaches to the airplane and it provides strength for attachment purposes (mainly).

P.S.

Use balsa you will thank yourself in the morning.

P.P.S.
If you dont use balsa use coroplast.