First be certain you can shift into big-big with out forcing it. This ability is absolutely essential for safety. If you can and there is still enough slack chain to allow removal of 1" (two half links) you can shorten it again. Otherwise leave it alone and avoid small-small, for which there is no use anyway. You have a short cage rear derailleur and what appears to be a compact crank. That along with the wide range cassette may have exceeded the rear derailleur's wrap capacity. If so there is nothing you can do but avoid small-small.