First thing, seam all the rolled edges by hand to make a flat seam, no ridge, looking good from the purl side which is the outside. Working from the knit side, with purl sides together, taking the longest existing yarn tail, go into the half outside edge
stitch/loop/bar on the side across, go down one row, into same side from outside, across to corresponding row of first side. Continue like this, going into each stitch/row only once.
I prefer to do long seams, like the side
seam and underarm, on the machine. For this one, I’m using my ‘Franky’ method,
with the chain appearing on the knit side.
https://knitwords.blogspot.com/2021/03/she-likes-it.html
Purl side facing, hang the first side, evenly, without
stretching, picking up half of the edge stitch/bar. Hanging the second side, knit side facing you (purl sides are together) use the loose row in the pattern to line up with the one
already hung to get the seams to match perfectly. Bring needles out and manually knit very loose row -pull stitch back at least half an inch! Carefully chain off.
which you prefer and make sure that your hand knit row is loose enough for the chain cast off – on mine, that stitch is pulled back a half inch! Looks too big as you’re doing it, but it needs to be that big to pull down for the length of the seam and allow the pieces to open out flat without bunching.
Hope you like your finished product – if you do, make it again and use another easy stitch pattern from ‘The Handbook for Manual Machine Knitters’, one of the plain lace ones like ‘posies’ or a simple tuck like ‘sweet pea’ – or even make it plain, without the needles out of work – you’ll be amazed at how much you learn by remaking something! Just knit and have fun!