Hi Danielle,
Ugh! I hate when that happens. 🙁 It really depends on the cake, the temperature of everything, etc.
If you have time…put the cake in the freezer right now! Leave the frosting out so it’s room temp and have the cake be frozen…or as cold as possible when you frost. Some crumbs with still come off, but it shouldn’t be chunks. Also, being generous with the frosting helps from the crumb coat. So, put a generous amount of room temperature frosting on a COLD cake. Then, put the cake back in the fridge or freezer is possible to get the crumb coat frosting to harden some. Then, frost over it.

Just saw these comments! Glad you figured it out. For making the cake, no, I didn’t have hardly any leftover cake. I used the everything (well, except for some small pieces that got “shaved” off). The 9×13 is the bottom base, plus a good chunk up front. I used the entire loaf pan cake to make the decks and part of the rounds on the front. The pieces you see for the island were basically my “leftovers”. I only made the island because I had those leftovers (it wasn’t part of my original plan). Hope that helps!