I looked at your pattern and figured out how I would do it.
Your pattern begins cast on 136. 12 of those are for the border (6 each side), so subtract 12 from 136 and you have 124 left. Divide that by 4 squares across each row and you have 31 stitches in each square. From looking at the pattern I would put 45 rows in each square.
So for the solid squares cast on 31 and work 45 rows of St st, beginning with a knit row. Cast off. Make 10 of those.
For the heart squares, here is how they work. (Make 10)
Cast on 31. Beginning with a knit row work 6 rows of St st which would make you ready to begin the heart on a RS row.
Row 7: K15, YO, SSK, k14.
Row 8 and all even rows: Purl back. You will always have 31 stitches except after row 37 when you will have 33 sts.
Row 9: K13, k2tog, YO, k1, YO, SSK, k13.
Row 11: K12, k2tog, YO, k3, YO, SSK, k12.
Row 13: K11, k2tog, YO, k5, YO, SSK, k11.
Row 15: K10, k2tog, YO, k7, YO, SSK, k10.
Row 17: K9, k2tog, YO, k9, YO, SSK, k9.
Row 19: K8, k2tog, YO, k11, YO, SSK, k8.
Row 21: K7, k2tog, YO, k13, YO, SSK, k7.
Row 23: K6, k2tog, YO, k15, YO, SSK, k6.
Row 25: K5, k2tog, YO, k17, YO, SSK, k5.
Row 27: K4, k2tog, YO, k19, YO, SSK, k4.
Row 29: K3, k2tog, YO, k21, YO, SSK, k3.
Row 31: K4, SSK, YO, K9, YO, SSK, k8, YO, k2tog, k4.
Row 33: K5, SSK, YO, k5, k2tog, YO, k3, YO, ssk, k5, YO, k2tog, k5.
Row 35: K6, SSK, YO, k3, k2tog, YO, k5, YO, SSK, k3, YO, k2tog, k6.
Row 37: K7, SSK, YO, k1, YO, k2tog, YO, k7, YO, SSK, YO, k1, YO, k2tog, k7. (33 sts)
Row 39: K9, k2tog, k11, k2tog, k9. (31 sts)
Work 6 more rows in St st and bind off.
Sew all the squares together using mattress stitch. Then I'd pick up the stitches along each side and knit the border I wanted, then pick up along the ends including the edges of the side borders and work the end borders as desired. It looks like they used double moss stitch.
I hope this helps and you will get it figured out.
Edited to add: I forgot to consider the seams would take up a stitch on each side and at the ends. So you might want to add two more stitches and two more rows.