Full throttle at engine start

I took the boat out this weekend to the river very excited after I just had it serviced. They replaced a sensor in the oil tank as the oil light was coming on at high rpms when I last used it. He also replaced a panel located behind the control panel as there were a lot of terminals that were very corroded and cleaning them would not have been enough to prevent future problems. As I launched I went to back up and touched the throttle. The engine accelerated suddenly in reverse to such degree that I had to turn it off. While Off I tried moving the throttle. Then, every time I turn it on it goes to full. I'm thinking a broken throt cable or other. Any ideas? What a scare!!!