I have found that only certain brand names of cling wrap actually cling to a bowl. You do have to stretch it slightly, as a PP said.
Many other brands only cling to the wrap itself, so you have to use lots of it and pretty much encase the bowl in plastic wrap. You have to go all the way around the bowl, top and bottom, at least with the first piece. Sometimes that will be enough of a base that the rest will stick.