Advice on wetsuit HELP

Right i have a wetsuit as per this morning, it was bought for me it is not completely skin tight in some areas, a few little sags that you cant really see but i know they are there, does the wetsuit have to be completely tight or can there be a fair amount of give to it? Where shall i draw the line and wat would be the effects if it was slightly too big? Thanks respond asap as i wanna use it tomoz?