Lucille Dress - Muslin

I made the muslin today, and I was fast too! I didn't do the collar (I don't think I've ever made a complete muslin, I usually only do one sleeve, or even just one half of the piece), since I wasn't using a fabric that drapes as nicely as the wool crepe I'm using (I just can't afford anything else than muslin, even that it kind of expensive in switzerland) I don't think the collar would've looked good anyway.

It's definitely not the most flattering thing I've ever made, but I have quite a few snug sheath dresses already, plus it's the Lucille Bluth Dress!! Not the Lindsay Fünke Dress.

I do think it looks better in real life than in pictures, but there's still something about the sleeves that I don't quite like. I think it's the folds that radiate from the armpit (never thought I'd use "radiate" and "armpit" in the same sentence...), as visible in the first picture. But I don't know how those folds will look when I make it with wool crepe. And I want this to be a comfy dress, a dress that I'd wear on a cold day, when I'd rather wear my I <3 NY sweatshirt than a sheath dress but still want to look put together (because the fabric is so gorgeous!), so I don't want the sleeves to be too tight.

The sleeve has a dart in it, so I'm thinking there might be a way to adjust the pattern, so that the weird folds are gone? Or maybe I need to change the side/sleeve-seam?

Or maybe there's not really a problem, cause the wool crepe will be heavy enough to not bunch up like the muslin does?

Well, I only just started pre-treating my fabric (and it will take a while, working in small sections) so I have some time to think about it...