The things in sushi that you have to worry about are rice, "spicy" sauce (which is mayo mixed with hot sauce), and tempura things. Remember that soy sauce will make you retain some water tomorrow anyway, so don't stress out if you jump up a pound or so when you step on the scale next. It'll go away once the salt gets washed out.
Sushi is the fish with little rice balls under it. Sashimi is the plain sliced fish. Then you have rolls. There are a MILLION kinds of delicious rolls. Some of them are rice-less, too. I have heard that you can request your rolls be made with less rice, although I've never personally done this.
So read the descriptions carefully. Avoid anything "spicy" or "crunchy" for the most part. If you like sashimi (and can afford it) load up on that. Have miso soup, which has practically no calories at all, and a lettuce salad with the ginger dressing. Ginger dressings are usually quite low in calories, as well -- nothing at all like ranch or other creamy dressings.
Or make it your cheat meal if you have one
I get GOOD sushi so rarely that I tend to just get what looks delicious and then cut a few calories the next day.