Modern Vespa

I recently bought a used GT200. First I was just riding it for two or three miles a day. When I felt more comfortable with it I decided to go for a longer ride. The ride was about 10 miles and when I decided to go back home I noticed that the temperature gauge moved past the half line, then the fan went off and I was aware of what was happening; however, when I beat the traffic the gauge came down to the half line(normal temperature).
So I checked the coolant reservoir and noticed that it did not have sufficient coolant, since we're in the middle of the summer I simply added distilled water so see if that well take care of the problem. Today I went for a ride and it seems like the problem got better but it's still over heating a bit. Please help!

has the temperature gauge gone into the red? if it hasn't, then you're not overheating. It's quite normal for the temperature to creep up past the half way mark and the fans to come on in warmer weather, especially if you're riding in stop and go traffic.

distilled water is ok as a quick fix but you should replace it as soon as you can with a 50:50 glycol/de-ionised water mixture.

It just passed the line in the middle. Luckly it didn't made it to the red zone. Thanks.