you do NOT HAVE TO PRE-WASH ALL OF YOUR FABRICS.
Some people do, some don't-- all make great quilts...the only reason to really (stress) over pre-washing is if you have a fabric that may run (bleed)...and you can test as you go along for those...checking reds (which are the bigest culprits)or handdyes/batiks;;;
i would not be starting over, there is nothing wrong with the 1 1/2" squares you already have!