are you lowering your presser foot? it should be lowered, feed dogs down- and yes, your stitch length will depend on how fast you move the fabric around in relation with the machine speed.==if your stitches are too big either slow down how fast you are moving your sandwich or speed up how fast the machine is going. (and vise-versa)
Practice on a small practice piece before working on a real project.
some people find it easier if wearing gloves with little gripper dots on them...there are lightweight ones available in lqs and craft stores or some people use gardening gloves.