Fun pretty square! The pattern cautions to make sure the FPDCs are loose and long enough to keep from pulling the sides in. Mine was not loose enough so added hdc in the middle of Rnd 7 to put back in shape.

Added Rnds 7- 9 to make 6”:
Rnd 7: (Sc, ch 2, sc) in corner, * sc next 2, (sc2tog, sc next 2) twice , hdc next 5, rep between and ] around; sl st in 1st st to join
Rnd 8: (2 hdc, ch 2, 2 hdc) in corner, hdc in each st around, sl st in 1st st to join
Rnd 9:(Sc, ch 2, sc) in corner, (sc next, sc2tog) three times, sc in next 3, (FPdc in Rnd 7 hdc, sk st, sc in next st) three times, (sc in next, sc2tog), repeat between and * around, sl st in 1st st to join.