How to create the finish line in SRB2Kart?

I'm trying to make maps, but the finish line is too fast, going from 1 to 3 very quickly, and with one lap completed. I can never get the finish line to work properly. The most I've managed is to do half a lap and run the track in reverse, completing the 3 laps that way. I'd like to know how to make the finish lines work correctly.