I don't know what the sushi is like at the Blue Water Grill but I know that my first experience with Japanese cuisine was in Japan. I hadn't long ended a spell (nearly 20 years) of vegetarianism and veganism.
I was very apprehensive and felt a lot like you. I could just about cope with it cooked but I didn't think I could handle it raw. How wrong I was. I am a huge fan of Japanese food now but in no way an expert. I love raw fish and don't really care for sushi (with rice)that much, preferring sashimi (plain raw fish). The best way to get in to it, in my experience, is to go with someone who really understands the food, the textures, the flavours and the correct way it should be eaten. There is so much more pleasure to Japanese food than just being served and eating. Given how fresh the fish can be in Belize, I cannot wait to try the sushi, sashimi or any other variation. Do remember that smoked salmon is a type of raw fish. Not to mention that there are a whole lot of wonderful cooked Japanese dishes too. Of the things I tried the two I couldn't cope with were dried flying fish. They were some rare flying fish that were dried in the sun whole. A real delicacy. I couldn't face them. I tried salmon roe (otherwise known as poor man's caviar) and I thought it was disgusting.
The USA has adapted a whole load of ways to make sushi more palatable for the western taste bud. I am sure you will find that there are plenty of things you can have at the Blue Water Grill that you will like. I ate there in December for the first time and really enjoyed their pan asian twist.