I worked popcorn stitches instead of the clusters.

Spike Border
1st Round Spikes: skip first stitch, “dc5, long dc in next stitch”, repeat to end of side, dc2, ch2, dc2 in corner, repeat between the brackets.

2nd Round Spikes: dc4, (long dc in next stitch, dc5) across side to last long dc followed by dc4 dc2, ch2, dc2 in the corners, repeat.

3rd Round Spikes: dc3, (long dc in next stitch, dc5) across to the last long dc followed by dc3 dc2, ch2, dc2 in the corners, repeat around.

Just FYI, the designer uses the v-stitch but calls them shell stitch.