I'm pretty new at this myself (just started last year) but haven't honestly found sashing to be difficult. However, since OP has said she doesn't have access to more fabric, I'd definitely agree with offsetting the columns and maybe with what you would have to trim off, add it back to the top of the column so it remains roughly the correct length as the others. It'll be slightly smaller because of the new seam, but less than if you had to trim every column.