I always tend to 'add a bit just in case too' It really comes in handy when I get a brainstorm and go off on a tangent or decide to enlarge the quilt. I have never met a pattern that I could not make more difficult
. This also gives me the chance to make an audition block of the real fabrics. There have been times that I just hate one of the fabrics once the block is put together, or that a glaring error will raise its ugly head.
I also always measure and compare the yardage as soon as I get a kit. That is when shortages are really frustrating!!