If you are not comfortable, either get an experienced captain you know or even hire one for a few hours. Have them show you how to use the throttles to spin the boat, back down, parallel dock and fore/aft docking at slips if possible.
Then go out and practice practice practice. When I got my first twin, I just did what you did. Got some advice and went at it. I splashed the boat very early in the season, only a very few boats at the docks. For two weekends Sat and Sun I went out the channel to open water, went back in docked and repeated and repeated until I felt comfortable. The first year I would be nervous coming in, but those around me would help and after that I was fine. It is all about a little knowlege, confidence and experience. You'll get it.