Base rnd, each side: Multiple of 3 + 2 + corner sts.
Begin 3 sts to left of corner st.
Rnd 1: Ch 3 (counts as dc), *ch 5, dc in 5th ch from hook, skip 2 sts**, [dc in next st, ch 5, dc in 5th ch from hook, skip 2 sts] to corner st, (dc, ch 5, dc in 5th ch from hook, dc) in corner st; rep from * around, ending last rep at **, join with slip st to top of ch-3. Fasten off.
To keep your yarn from rolling around, gathering dust as you work, use a ball winder or learn to wind center-pull balls by hand. A center-pull ball stays put nicely.