I would take off the added borders on just one block to see if I could true up the block. Panels like this are often off-square, usually because fabric is stretched and distorted as it is wound onto bolts. They are also often printed off-grain. Usually you can "block" them into an appropriate square shape using spray starch, a pinnable ironing board, and an iron. Sharon Schamber used to have some Youtube videos on how to square up applique blocks, but I can't find them.
Basically, what you do is place an outlined square on your ironing board. I would do this by drawing the square the block should be on the matte side of some freezer paper, then iron the shiny side of the freezer paper to the ironing board. Saturate the block with starch, either a heavy spray starch or a 1:1 solution of Sta-Flo liquid laundry starch and water. You do not want the block dripping wet because of the freezer paper, so give it a few minutes so the fabric fibers have a chance to absorb as much starch as they can, then wipe off any excess with a finger. Position the block on the square outline and start pinning. I would start in the corners, then fill in with pins about 1" apart along all edges (starting with a pin in the middle of an edge, and working evenly out to the corners). Try to smooth out ripples with a finger. At this point I would let it dry completely. When dry, remove pins as necessary so you can steam *press* (not iron back and forth) the block. This should square it enough to proceed with making your quilt.
You will want to use at least a moderate amount of quilting on those blocks to keep them squared. If you were to just outline quilt the blocks, when the quilt is washed, the block fabric might develop ripples again. To keep the blocks squared, be sure to include some quilting inside the blocks as well as around them. The quilting will secure their positioning.
You may not be able to get the blocks perfectly square, but you should be able to get them squared up enough to use in a quilt without drawing attention to squareness.