Mamabear61 has the right idea. Most plaids and strips don't read straight. THis is probably old info so please be understanding.
I never rotory cut anything with a stripe. I always hand cut following a selected line and then pin to ironing board, dampen a little and work it to be straight, repining as you need to. Let it dry and you are ready to work with it.
If the fabric is too crooked, return it if possible, which I doubt 'cause this problem usually comes with the territory of the way stripes and plaids work.
Hope it works out for you.
peace