oh no! That is a problem. Do the armholes fit? If it’s just the sleeve and not the armhole, you can cut from the wrist, up the center, but not all the way to the sleeve cap and then spread the pattern apart to increase the width. This method adds more to the bottom of the sleeve than the top portion so you don’t change the armhole dimension. If it’s also at the armhole, you’ll want to check our increase a sleeve width video because this will show you how to increase the sleeve width but it also alters the sleeve cap and if it’s by a significant amount, you’ll also have to alter the armhole on the bodice. But if I were you, definitely experiment on muslin so you don’t use your expensive fabric until you have the perfect fit.