Boat too slow

[Aquaholic101]

I bought a used 14 ft Sea & sport w/ 25 merc to beat around the back water. New spark plugs, new bottom paint. Boat runs great but it wont get up on a plane, just seems to drag through the water wide open. The only thing I could think of is maybe the wrong prop is on the engine. Any suggestings, thoughts?
Vinny