As Mary Grace said, end with a RS (right side) row but do not break yarn. Chain one and rotate your blanket clock wise so that the rows are now aligned like columns and what was your Top Left Corner is now on the top right. The RS is still facing you; now work two sc around the post of each double crochet at what is now the "top" of each "column/row."
Okay, some of the ending double crochets will actually be the 3 chain turning chains that counted as the first dc of the rows. You treat them the same, just put two single crochet stitches across the end of each row (rows that were turned to run up and down like columns) as you work the side of the blanket.
When you reach the next corner (Bottom Left Corner of the Blanket) you need three single crochets in the same corner stitch to turn the corner and again rotate the blanket (it will now be Bottom Row Up, with RS facing you still). SC in each stitch across (72 stitches) then 3 sc in the last(corner) stitch and again rotate the blanket.
Continue like you did across the other ends of the blanket rows. Treat the post of the dc the same as the chain 3 turning chains and put 2 sc in the end of each row across to the Top Right Corner fo the blanket. Three sc in the corner and rotate again (blanket is now top row up again.)
SC in the top of each DC across to the last stitch, then 2 SC in the last stitch. Slip stitch to join with the first SC on the edge. Break yarn and weave in end.
Did a long hand translation help? I hope so; good luck and please share a picture when you've completed your blanket.