I use pre-cuts all the time - I would not worry about squaring them up before using them - if your overall blocks look a little wonky then you could do some trimming - but I love pre-cuts and use them all the time - but I only purchase Moda, Riley Blake or Robert Kaufman pre-cuts - these are the only ones I use and never had a problem. Also, the pattern is specifically written for those pre-cuts and I think you will be happy using them right out of the box - its really the advantage to pre-cuts - they should be ready to go.