Dig your game boy out of the closet and listen to all the pokemon tracks. I recommend you analyze those. They mostly have catchy melodies that can be looped without people getting tired of them. If your game only plays that one song over and over, and doesnt switch songs at all, then i recommend what thatboy said: five minutes of music or so that can be looped. Might be cool to just do variations on a main theme. So like maybe the theme plays, then there's sort of a bridge, and then it plays again but in a different octave, or by different instruments. Still, go on youtube and listen to a lot of final fantasy music or pokemon. Harvest Moon and Animal Crossing should be pretty useful stylistically.
Hope this helps! :D
--Miggy Torres