Now I see where I went wrong. I did pin baste, about 4-5 inches apart. I didn't starch. But the real problem, I think, was stretching. Some of the places where blocks came together were hard to sew through (the stitches there are so tiny) and I had to pull the quilt through or hold the fabric flat from the sides (that isn't clear but I don't know how else to describe it).
So I guess I will take out the line of stitches that had the problem. I wonder if I can avoid taking out all of the stitches in the whole quilt, as I couldn't believe how difficult it was to take them out (Are there any good techniques for taking stitches out?). Then spray with starch (without ironing?) . Then start again from the center, maybe using Dina's method of making boxes? Also, I didn't know about the foot pressure. The machine has a knob to change it but I didn't know what it was for, or, how you know it is the right setting.
What stit