Trim all four sides of the fabric to make sure the edges are straight and lined up with the plaid. Gently pinch the edge of the fabric and slide your hand down it to remove any loose fuzzies from the sherpa.
Turn up each edge 1.5 inches and pin, leaving 6 inches around each corner unpinned.
Fold in the corner at a diagonal, matching where the edges will be turned up to.
Fold in the edges over the corner to create a mitered corner and pin.
Place the fabric on your sewing machine and line the needle up about 1/8 to 1/4 of an inch from the raw edge. Smooth the edge of the sherpa to the right.
Sew all the way around the blanket. At each corner, sew down to the corner then turn around and sew back up to the raw edge.
When you get to where you started, backstitch to secure, then trim the threads. Wash the blanket on delicate, cold water, with a small amount of detergent and white vinegar instead of fabric softener. Dry on low heat just until dry.