i am making a tube quilt and find that it is important to watch the fabric and not the needle. Also do short sections. Don't try and do the entire length of whatever you are sewing in one sweep. Stop and readjust as needed.
I tend to think folks think that it is a guide it will know where the fabric should go. Not so. Take it slow. Alo when sewing be sure you can barely see the piece underneith. Just the edge of the under iece. Then both will be accurate.