Your little island raising above the 100 yr flood level means your building is NOT in the flood plain. Flood zone A = 100 yr flood plain. Your building is above that, but older flood maps cannot show that detail due to their scale. That's the purpose of a LOMA, to ammend the map with a letter stating your building's elevation removes it from the special flood hazard area. While you might not need to worry about flood insurance on a barn according to todays laws, some day you might. And if you store things in the barn or use as a business, then a future loan with that as collateral would force flood insurance on it unless you have a LOMA. Now go online to FEMA.gov and apply for that LOMA while the elevation certificate is still handy. Good luck, and it's good to hear you got the permit!