I used circular needles instead of DPNs. There are a few adjustments I have to make:

First, I wanted to do provisional cast-on instead of picking up many stitches around the edges. So I used Judy’s Magic Cast-on to cast on double amount of stitches (I.e. 28 sts). I left half of the stitches on the cable of the circular needles, and made 12 rows of garter stitches with the remaining 14 sts. Next, I picked up 6 sts on the side edge, knit the 14 sts on the circular-needles’ cable, and then pick up another 6 sts on the opposite edge. Place a marker to mark the BOR. Following the pattern again, I worked 12 rows in Stockinette stitches.

Body
The body was just stockinette stitches in rounds except the two decrease rounds:

Rnd 13: skp, k10, k2tog, PM, k6, PM, skp, K10, k2tog, PM, k6.

Rnd 15: K12, SM, skp, k2, k2tog, SM, K12, SM, skp, k2, k2tog.

Make the holes for the backpack straps:
k3, yo, skp, k2, k2tog, yo, k3, SM, skp, yo, k2, SM, k3, yo, skp, k2, k2tog, yo, k3, SM, k2, yo, k2tog

Knit one more round, knitting the yarnovers from the previous rd.

In the next round, k to the 3rd marker. SM. k2. Start binding off from the last 2 sts before the BOR and until there are 16 sts remaining. k15, and ktbl. Remove markers along the way.

Flap
There was no adjustment being made. Just follow the pattern through.

Straps
I made an i-cord for the backpack straps. I also braided a tiny cord with 3 strands of yarn to tie up the backpack opening.