/cgl/ - Cosplay & EGL

Oh good, a sewing thread. I have a question.
So I'm still a beginner at sewing, but I always have the issue of my fabric sliding..as in, I could line the two fabrics up perfectly, but once i start sewing, the bottom fabric ends up somehow being longer and then it kind hangs off? How do I prevent this from happening?
I have a Kenmore limited edition 17 stitch machine. Pic related, my machine.

> brand
Kenmore
> model
Limited Edition 17 Stitch
> functions
17 built-in stitches and 64 stitch functions
One step buttonhole
Snap-on feet
> how long you've had it
4 years

>>7505541
One step buttonhole. Once I tried it, I was too spoiled to go back to anything else. Other than that, straight and zigzag (with adjustable stitch width) are all that I really need. Everything else is nice to have, but not required. Stitch settings are nice (so I don't need a serger) but you can improvise with adjustable zigzags if you don't have one.

Oh snap on feet are great, too. I used to sew on my grandmother's 15 year old Kenmore, and having screw the feet on and off was annoying.