I am knitting a sweater in seperate parts. The back section and the front section curl all along the sides. How do I flatten this out? Will weaving the front to the back at the side seams cause the curling to flatten out?
Yes, they’ll flatten out when you seam the edges together.
before the fact - you can prevent curling at the side seams by knitting across the right side rows as given in your pattern, and on the wrong/purl side row, slip the first and last stitch purlwise (or knit the first and last stitch, and purl all the rest, creating a one-stitch-wide garter stitch column up the sides.) Your work will lay so much flatter for you.
after the fact, yes, you will have to work it all out in blocking. you’ll have to shape and pin to the correct measurements. and then seam after having blocked the pieces.
I hope this helps out - if not this time, then next.