That's not a big concern for prototyping. It will reflow just fine. There might be a few solder balls rolling around afterward, maybe a bridge or two. Most of the time, this means your stencil apertures were too big, or that the cut-rate Chinese solder paste wasn't the bargain that it looked like on AliExpress.

Slump is a problem if you're trying to run a six-sigma process in a factory, of course, but that's not what's being discussed here.