I've never tried doing a bag from a pattern. I just
1) decide what size I want it to be, and whether I want the seam(s) on the side or the bottom.
2) cut outside and lining exactly the same size. I often use upholstery fabric or denim for the outside.
3) if not using heavy fabric also cut interfacing or batting the same size as well.
4) next cut 2 strips for handles 3" x desired length. For lightweight fabric also cut interfacing for handles. Or use the purchased webbing.
5) now cut your pocket pieces. These can be from contrasting fabric or from your same fabric.
Either cut fabric so fold is at top or cut two pieces the same size.
6) determine pocket placement and stitch to lining piece or outside being sure to backstitch at least 1" at upper corners.
7) fold straps in half lengthwise right sides together. If using interfacing have it on top when folding.
8) stitch one end and the long edge.
9) turn right side out and top stitch close to both long edges.
10) position handles at top of right side of outside fabric and stitch all the way across
11) place top of lining over handles right sides together, pin, turn over so you can see where you just stitched and stitch lining to outside with original stitching just inside the seam line.
12) open out your assembled piece and stitch so that outside will be stitched all the way around and lining will have a small opening for turning.
13) turn right side out and hand stitch opening closed.
14) top stitch near top edge.
15) enjoy your finished bag!
If you have questions PM me.