I am FAR from an expert at this but have been told as already mentioned to be sure it's level. Also, you can't have any lint (NONE) in the wheels , tracks etc. and must be sure there isn't even a tiny bit in your bobbin case. It helps if you can actually relax your hold on the machine and remember to breathe! Are you getting good stitches? I have a hard time with my machine tension every time I change threads. Good luck and don't give up! It really is fun. Get yourself some cheap fabric - you don't have to like it - and practice on it. Did you know that batting has a right and wrong side up? Maybe not all of it, but a lot does. Someone else will probably address that. Above all, have fun with it.
An after thought - don't wind the quilt and backing so tight things bounce off it. Too tight causes problems.