05 sportster

Hey I just purchased a 05 Seadoo Sportster about 4 weeks ago... I have taken the boat out every weekend since I got it... Problem is the gas guage isn't working properly... It stays on a quarter tank... I fill it up every time I go out but is there a easy fix for this or do I need to bring it into the dealer for them to look at it? I'm new to the boating world and have very little experience... Any help would be great! Thanks for your time