Iron your jersey fabric flat because it always has a tendency to curl. Iron up your desired hem before stitching. You need to iron jersey very gently to avoid stretching it.
Select zig-zag stitch on your machine. Ideally you want to use a ball point needle when sewing jersey. It prevents the jersey from laddering and stops the machine from skipping stitches.
Position your needle so one side of the zig-zag is just off the hem and the other side is on the hem. You might want to practice on a scrap first. Start stitching, being careful not to stretch the fabric as you sew. It always looks a little stretched when you finish sewing but a light press will improve the look.
I used thin jersey in this example so selected a number 9/70 needle and a wider stitch. You may want to experiment on a scrap first to find the right stitch width and needle for your fabric.
This technique is useful for sewing any weight of jersey fabric or knit fabrics – t-shirt material, sweat shirt fabric – basically anything stretchy.