Is there a mattress stitch for purl?

What I mean is, is there an invisible seaming stitch you can use for purl like the mattress stitch for knit? I’ve got a sweater sleeve I’m sewing up and its got a six row garter stitch at the hand end of the sleeve and I’d like to seam it up seamlessly but I can’t figure out how to do it, and searching this site and the internet hasn’t helped. I’m so close to having this sweater done (it was supposed to be a Christmas present. Its been a… learning experience).

Pick up the lower purl loop on one side and the upper purl loop on the other side and stitch it like mattress.

Thanks! Now I have a totally different problem… It seems the right front panel of the sweater (its a cardigan type deal for a 2 year old) is about an inch to an inch and a half longer than the back panel. Behold:

and a closeup:

Please tell me something can be done about this other than ‘reknit that section’ or ‘have a beer cuz you just wasted six months of your life and 86 bucks.’

When I first saw what I did I was like ‘dammit’ and took it to the knit store and asked them about it. ‘Oh no problem’ they said. ‘You can fix that when you block it after you seam it up’ (as they pulled and stretched the two panels to match up). It IS the same number of stitches, I’ll note, just different gauge I guess? I never paid attention to that part because I could never get it right (it was supposed to be four stitches to an inch. Four rows? Four whatever. So an inch square would be 16 stitches in four rows of four). I have no idea how off I was. I just knitted til the sides seemed to be the same length as the back/each other (I’m new at this, and the pattern wasn’t helpful much, even though its supposed to be a beginner pattern). This is my first sweater, before this all I’d made were two hats and two pairs of baby booties (one pair turned out perfectly, had eyelets and everything, just one was like half a size bigger than the other).

Anyway… help?

I would undo the seaming and block it to size and then seam it. A little hint ,when seaming always start at bottom of sweater and work towards arm hole.That way if you are a little off you can fudge it under the arm and no one will notice

I’d take out the seaming, and either block or attach the ends of each piece to each other and ease it to fit. I usually tie pieces of yarn along the seam edge to hold it in place.

And yes, definitely start at the bottom–at least you’ll know that it will match there.