and make sure your machine is clean. no dust "bunnies" under there.
loosely place your quilt around the needle and quilt an area .then stop when you can and shift the quilt as needed.
also move the quilt slowly and the foot pedal speed faster. if you move the qlt too fast you will get longer stitches.
good luck.

Thanks everybody for your replies, must try all that first!

The layout of the bobbin case has a lot to do with it, too. Machines that have vertical hooks and bobbin cases seem to FMQ better than ones that have (flat) horizontal hooks and cases. When they are vertical, the thread feeds straight up. When they are horizontal the thread has to take a bend, which makes the machine less useful for FMQ.

you might try unthreading everything and rethread the machine and the bobbin....try on some scrap first....also make sure you have the same thread in both places....and the needle is inserted correctly....just some things to check ...sure hope you find the problem....Good luck...:-)

Work on your tension, make sure you are not pulling or increasing the speed with your hands, re-thread, get a new bobbin, clean the machine, get a new needle....all things I have tried.

If kinda sounds like you are going to fast. Need to prctice and you will find the right speed Sometimes we hve a heavy foot. Slow down.