The quilting stitch should be one that you push the needle down through all layers, turn to the side only about 1/16 of an inch and bring the needle up through the top fabric.
Instead of taking a stitch straight down through layers and then (from the backing fabric) straight up through layers, take stitches only from the top....meaning the needle stays on top of the quilt stitching in an almost running-stitch fashion.
Instead of taking a stitch straight down through layers and then (from the backing fabric) straight up through layers, take stitches only from the top....meaning the needle stays on top of the quilt stitching in an almost running-stitch fashion.
The idea is to make your stitches close together and even.
Having said that, keep in mind that the nature of quilting allows for some variation of stitch size. And only practice brings uniformity of quilting stitches. So just keep going!
Click the link below to watch The Quilting Stitch, from start to finish.
https://www.youtube.com/watch?v=Kewhr2FcN30&t=2s
Questions? Ask them in the YouTube comment section.