I purchased a peter pan collar blouse from Urban Outfitters a few months ago, and though the fit wasn't quite perfect it was cute enough that I stuck with it. But after wearing it for a while its primary fit issue is starting to bug me: the arm holes aren't big enough! See picture for how it's cut. I could open up the seam on the tight end of the sleeve, but is there something I (or my tailor) can sew on the interior so it's not flapping open? Do you think any piece of similarly colored fabric will do, or would it be smart to go with some kind of elastic so I get that fitted look on the arm without it pinching like it does now?
Any advice is much appreciated.