You can finish off knitting three ways. If you would like to bind off or throw off, then just knit the first two stitches, insert your left needle into the first stitch you knitted and pull it over the next stitch so the first stitch is wrapped round the neck of the next stitch. Duplicate another stitch; pull on the stitch over it. So that you leave a long tail when you get to the final stitch, cut the yarn and then yank on upward the tail. If you already know all that but fear you will mess your sweater by mis-weaving in endings or blocking or seaming it wrong, stay tuned. If you get beyond the rinsing part, spread out the pieces to dry and pressed out the water, you can mess it. Pay no attention to what shape or size they finish up so they are nice and crooked. When you combine them if your fronts and back are different lengths, then they would not match up.
You could pin your pieces sprits with water, out the size let dry and moist. Or use gobs of steam with an iron held over the fabric. Leave the room. Your cat or dog will appreciate this marvelous toy you spread out for them. You can weave in ends or a few people especially cast on knitting weave them after before blocking. Some work yarn tails beneath bumps on the backside with yarn needle or a hook. Do not weave a tail via a white area or it is going to show through. Yarns may need with sewing thread or a dot of adhesive, nailed down and will slip back out. Some skim yarn ends through edges of lumps on the backside with a needle. If you prick your finger and bleed in your knitting, it might be taken by your spit out. Be quick before it dries.
Time for seaming
There are if you cannot make head or tails of this technique. Some people join pieces with a crochet chain stitch that may look very nice with the ideal size hook, yarn and tension or all wrong. If you do not redo a seam that is botched, trust everybody will understand. Some folks stitch Sweater pieces together using a machine. Ripping out this bad boy could be a nightmare. Buttons or zippers include a new area fraught with tragedy. If all this talk of possible disasters in finishing off knitting frightens you, you could always ball your job up, stuff it in a bag and hide it till you are feeling brave enough. Or hire somebody who can finish off knitting in the way so you wear your sweater.