Is that all the oil that got loose? There is 26 ounces of oil in the tranny, if that's indeed all that leaked out you shouldn't worry too much. Make sure all the oil is cleaned off of mechanism parts and then hook it up and have a wash!
If you want, you can drain the transmission, prop the machine to refill using air compressor oil. I wouldn't add new oil to the old, best to drain and refill with all new if desired.