Casting on

Hi.
I am having trouble casting onto an existing row of stitches without creating gaps.
It is above the thumb gusset for a mitten.
Thanks.

Have you tried the knit or cable COs?

I’ve tried casting on by knitting each stitch and instead of dropping the original stitch, keeping it on the needle.
(I know that picking up stitches is another way but for making deliberate gaps for design.)
I have not learned cable cast on.

I need to cast on 2 stitches to an existing row of stitches for the thumb gusset.

Then you can use the knitted cast on. There are videos for several ways on the Cast on page.