Chevron sweater

I am trying to knit a stocking stitch jumper with a slash neck made up of a rectangle for the front and another one for the back each knitted as a chevron in the following stages.

Starting with 1 or 3 stitches, increasing 1 stitch at each end and 2 in the centre on alternate rows until the desired width is reached. Then

Decreasing 1 stitch at each end and increasing 2 stitches in the middle on alternate rows until the desired height is reached. Then

Decreasing 1 stitch at the edge and knitting to the centre and decreasing 1 stitch in the centre then turning to complete both sides separately, one stitch being decreased on alternate rows at both the edge and centre edge until all stitches have been decreased. The other half is completed likewise. The result is usually a more or less straight bottom edge, straight sides, but a distinct shallow V shape along the top edge. I have also tried producing the rectangle starting the other way up starting with two separate pieces and then joining them knitting decreases in the centre and increases at the edges for the main part but the result is still the same with a v shape edge.

Please can anyone tell me how to get all the sides straight so the shape is rectangular and whether it is better to work with the increases for the chevron in the centre or at the edges?

Thank you.

The directions are correct for the questions you ask, just follow the pattern, so I don’t quite understand your concerns. :?? The increases in the center make the chevron, the increasing/decreasing along the edges shape the piece. Which pattern is it?