welcome from OK.
First you need to say how big is the applique, are you fusing or doing needle turn applique?
either way, but especially for needle turn, I would start with a block that is about 3" larger than what I want it to end up being. THat way should anything go wrong, it gives me plenty of space to square up. Also should I need to hoop it, I have plenty to put in the hoop while I work on it!