What type of batting are you using?
It is hard to get NO puckers if you are using a medium- or higher-loft poly batting (which may still say "low loft" on the package).
Are you stitching on a regular home machine? To SITD on one of my home machines, I baste with safety pins on either side of the line I'm going to stitch; this machine has dual feed so I don't need a lot of pins. For the other machine, I thread-baste right next to the line I'm going to stitch. For both methods, when I'm sewing I keep one hand under the quilt to smooth the underside as I feed it through the machine.
Last, how puckered is it? A pucker here and there isn't a dreadful thing. I personally only rip out the big ones or if there are several in a row that would cause a problem elsewhere. Quilts have some texture and depth, and it would be odd if there were never a pucker anywhere.