I don't know if a long stitch is actually caused by skipping a stitch but my feeling is that the stitches are far apart. Any way of knowing if it has to go into the shop? They just looked it all over a month or so ago, but, I didn't know enough to bring my BSR with the machine. They didn't ask either.
As you are new to the technique I would say you are moving the fabric to fast to slow. I do find it is better to go faster than slow.