With A, ch 49. Sc in 2nd ch from hook and in each ch across; turn – 48 sts. Work 64 more rows sc (5 total). Fasten off A.
Rnd 1 With RS facing, join B in first st at right edge of work. Work 3 sc in first st, sc in each st across row to last st, 3 sc in last st; turn to side, sc evenly spaced in row-end sts across long edge; 3 sc in first ch of foundation ch, sc in each ch of foundation ch to last ch, 3 sc in last ch; sc evenly spaced in row-end sts of remaining edge; join with slip st in top of first sc; turn.
Rnds 2-4 Ch 1, sc in each sc around entire edge, working 3 sc in each corner st; join with slip st in first sc; turn.
Fasten off B. Weave in ends.