A flat, wrinkle free straight border is a very common option!
The hardest part of this is finding a place to lay our quilt flat.
If we’re using a carpeted floor, try not to stretch the fabric, instead you want to smooth out the wrinkles.
Measure the width in 3 places, top, middle, bottom, and the length, left, middle, and right.
Use the number that is closest to the average of the 3 numbers.
Or multiply the width each block is supposed to be by the number of blocks. Don’t include the seam allowance only the finished quilt block size.
Select the number that comes closest and cut or cut and pieced your borders to the length required.