Why the extra fabric at the armpit of my sweater

I am knitting the Evening in the Village turtleneck by Two of Wands.

When I was knitting the arms, I made a big mistake and decided to push on instead of frogging. The pattern tells you to knit in pattern for 6 cm and then decrease on both ends of a RS row every 8 rows…well, I thought it said decrease on both ends of every RS row…So for 12 rows thats what I did. until I caught myself. I had unfortunately rapidly decreased. And instead of fixing my mistake, I thought well I don’t like big sleeves anyway…so instead I knitted 48 rows with no decreases. Essentially, I got to the length I should be at given the number of stiches I had left. I then decreased on each end of a RS row every four rows (bc again, I don’t like big sleeves) until I got to the number of total stitches left I should have.

I lightly blocked my pieces and then seamed up my arm. When I put it on…I realized some unfortunate extra fabric at my armpit. It’s puckering at the part where we knit in pattern for 6 cm, which is then followed by the rapid decreases.

Is it puckering because of my rapid decreases? Or because I seamed it incorrectly?

What do you think is a reasonable way to fix it? Should I frog the sleeves and redo them correctly this time? Re-seam? Steek?

It’s the rapid decreases at the top of the sleeve that are causing the extra fabric. You could either steek or reknit the sleeve. Steeking would be relatively easy as long as you like the taper on the rest of the sleeve. You’d only have to steek the first several rows where the rapid decrease occurred. There are several ways of reinforcing the steek either by machine sewing or by hand. Here’s one with hand stitching.

You’ve knit such a pretty sweater. It should be one that you enjoy wearing.