Hi! I want to know if dolphins are friendly?

I'm going to "Swim with the dolphins" tomorrow at Sentosa and I'm a bit afraid because I just searched about the 'friendliness' of dolphins and there were people saying they were not, but we think they are because of their curiousity but some of them are agressive. Ok, so I thought, "What?!". Then I got really shocked when I saw actual videos of dolphins suddenly attacking humans, there was one at the dolphin school and another at a doentary. So I'm just wondering, do I have a reason to be scared tomorrow?