it should be moist... leave the bag wrapped tight until you have a considerable amount of colonization.. then the bag will want to inflate on its own..
if you have any stale air in the bag before you inoculate THAT could lead to contamination even if it has a filter patch and was sterilized.
if the bag doesnt have a self healing injection point you can make your own by putting a dime sized spot of silicone gel (clean spot of bag first with alcohol)let dry, shoot up through that.