It is a throttle linkage problem. My dad's boat had that happen. It was actually a problem with the control box, it'd work fine about 99% of the time but if you pinned it and pushed just a little too hard the shift lever would go past a 90 degree position. When it would do this the throttle cable would be stuck at WOT and wouldn't return unless you fiddled with it a bit going back and forth and finally it would eventually return. I'd suggest since it's your first rig to take it in and have it looked at. It could be something else as well, but I'd be guessing that's what it is. Also, if you run it at any point between now and then see if you can run it fine without pinning it or pushing it past where the WOT stop should be.