common (ailment) with panels, they are seldom straight. small-pillow panels may be but the larger the center-the more 'skewed' they tend to be. you can try to block them or you can simply cut off the outer 'frames' and square up the picture area before adding your own borders, or, you can 'fudge' the sizes of your added borders in small amounts so it is not really noticeable but one side may be 1/2" wider than other side-type of fix. I've done all of the above in the past- it does not stop me from picking up a panel I want- I just take a look at it & decide which method will be easiest, give me the best outcome- then go from there- seldom do I ever get to actually use what ever the 'frame' is- except I have cut the frames off before- then re-used them by cutting them straight & incorporating them back into the design after squaring up the center.