Here are the instructions from the pattern for sewing the base to the body:
Sew base to tube, ridge-to-ridge, 2 times,1 base ridge to 2 body ridges, * ridge-to-ridge 5 times, 1 base ridge to 2 body ridges,* rep from * to * around until last 2 ridges; sew ridge-to-ridge. Note This gives bag a bit of fullness
The "ridges" they are talking about are the garter st ridges...so, sew 1 base ridge to 2 body ridges TWICE, then you start repeating the part that's between the *'s....sew one ridge to one ridge 5 times, then 1 base to 2 body ridges once, then 1-to-1 five times, 1-to-2 once, etc., until there are only 2 ridges on each side left. Then sew two-to-two..