Denise ,I do mark my quilts when I need to ,I use a white chalk pencil or my Frixion pen which ever works best. I do run a FMQ group here and hope you will come and join us .I have lots of info there and you can go back and looks at some of the things we do for practice . Feel free to ask any questions and if I don't know the answer I'll find out for you . I do highly recommend you take the class offered by Leah Day on the Crafty web site .she is a fabulous teacher and makes it very simple for you and this is done in video and and you can ask questions,as well .great class .I and a lot of us here have taken this .
EAT!! SLEEP !! QUILT!!
The way I was taught (on-line) to square up quilts was to measure the middle from side to side and use that as your measurement for cutting binding (or the final border). I either ease the edge or slightly stretch it to fit the outer border and it comes out square each time (or within 1/2" which I consider good enough). I had one quilt that was over 2" off across the top as the squares were on the diagonal. This is probably not the way to do it, but I started at the center of the side and trimmed up, ending at 3/4" at the top. Did this on both sides, and then cut the binding according to the measurment in the middle and eased everything in. When done, it was impossible to tell I'd sliced that amount off. Of course, that wouldn't work on one with a narrow border unless you did the slicing before putting the border on.