I just started knitting this weekend and am making a scarf. The pattern calls for 4 rows garter, 8 rows St. Then repeated many times. The problem is, when I start the St and purl the first row, it starts to feel tight. By the time I finish the next knit and start the next purl, I can't move the needles anymore! I don't think I'm pulling the yarn tight, so I'm not sure what's happening. I've unraveled and started again about 5 times, same thing each time...any advice?? Thanks!!