I am just starting out with my pe770. Sometimes it works great and other times I have can’t figure it out. I’m working on a letter B now, it lays out the first set of stitches then comes back with a satin stitch but that satin stitch doesn’t completely cover the first lay out stitch. I’m not sure how to fix this. I’ve slowed the machine down and it was worse. 

Sounds like it may be a problem with your stitch file, not your machine. did you create the file or download from someone else? May want to check the quality of the stitches in another program....like sew art pro.

Just my input for what its worth!!

It would be great if you could upload a picture so we can more easily determine what´s going on.