Oh dear i know exactly how you feel. I made a minecraft about six months ago, a giant 10" and 8". I cut out a lot of my squares a few days before i planned to use them so they were nice and hard. I mixed half sugar paste and fondant and mixed with a bit of tylos and cut them out with a square cutter, i did try other ways of cutting the squares but the cutter definitely looked neater. All my squares were half an inch big, which ment they would fit each side of the cake perfectly square to square. I left some squares to cut up on the day which worked well as there were one of two spaces that were a little tight which ment they squeezed in easier as they were softer.
I think the main thing is make sure the sides of your cake are dead straight then you should be fine. Good luck :) x
ellie's elegant cakery
