How did you put ordnance on it? When I pull up the arming menu I don't see any inventory to load on it. Do I have to edit something?
Dido what Kramer and EinsteinEP said. You first need to set the type of mission. Then go down at the bottom of the page and hit the "New Loadout" button, name it what you want. Then put mouse over each box in line with that loadout name and under the aircraft, where each pylon is. Right click and it will give you your options as to what can go under that pylon. Once done, make sure you save mission and you can use that loadout for other missions as well.
Pretty neat actually. You can create a number of loadouts and the mission editor will stop you from putting something on there that cannot be for the type of mission or that pylon.