I assume its a 3HP, which maybe a little light. I use to own a yacht called a Red Jacket, that was an 18ft trailer sailer which had a 6HP with a displacement prop.
Your seagull would probably be fine on windless days, it's the windy days you may have problems, especially if you are trying to make headway against the prevailing breeze. A 3hp may not have enough grunt to push you thru any sort of chop.
I would stick with what you have for a while and work out whether it is ok or you need to upgrade. You'll soon work out whether you need to upgrade.