Gauge problem

I’m starting the Altostratus cardigan using Malabrigo sock. The pattern gauge is 4 sts. per inch on 8s. I’m getting about 5.5 on 9s and about 5 on 10s. I don’t get 4 until I go all the way up to 11. The sweater is all garter stitch and I’m concerned that if I use 11 it will be too stretchy and sloppy looking. It’s a pretty stretchy sweater anyway and the pattern recommends making a size 2-3 inches smaller than what you would normally wear. If I stick with size 9 needles I don’t know whether I should still make the smaller size or my actual size. I don’t know how much difference 1.5 sts will make overall.

If you multiple 1½ sts per 4" over 36" that would be 13½ sts or more than a couple inches too small. Did you wash and dry your swatch to see if the sts relaxed at all? That gauge would be pretty stretchy for sock yarn in the first place, it’s a heavy worsted/aran weight gauge.

Since it’s a raglan you could cast on for your regular size and increase until the back sts measure about half what you want the finished measurement to be. Then try it on, see if the yoke is long enough and that it’ll fit okay. It’s not supposed to meet in the front at all, so that’s why the back measurement will be the one you go by I think.