You've probably noticed this already, but there are a number of small holes where the strap attaches to the clasp on that side. Only one pair of holes is used by the pin that secures the links to the buckle. You can try and move the link to the outermost holes on the strap to see if this reduces the 'gap' somewhat. It'll also increase the size of the band a bit, so you may then have to remove one link to compensate.