Round 5 doesn’t make sense to me. The round count reflects a stitch increase but there is no place in the directions that has a dc x 2 in a stitch to create that increase.

Therefore, I am working my:
popcorn stitch in the top of the fpdc in the previous round, dc in next stitch, 2dc in top of popcorn stitch in round 4 repeat around.

This will give you the 12 popcorns & 36 dc that the pattern suggests.

Corners
I worked ch2 in the corners.
2dc, ch2, 2dc