I also make mine larger, like if it says to make the squares 3 7/8", I will make mine at least 4", and often even a little larger than that. I then go on and make my hst, and then trim it to the right size. I know this wastes a little bit of fabric, but it is well worth it to me to get the hst consistently the right size...otherwise I have to try and iron them even, or go back and take them out and try and re-sew them...I actually have done the latter, before I decided much better for me to start with my squares larger.
Good luck to you,
Kif