New Gas Tank Sending Unit Leaks

Hey guys, I just replaced my gas tank sending unit in my 69 Cuda last weekend. The new unit works, it is a nice feeling knowing how much gas you have in your tank! Filled it up and went to a show last weekend, no problems. Which, brings me to the problem. Went out today to get my car ready for another show this weekend. I noticed a strong odor of gas. I look under the car and there is a puddle of gas on the concrete. I could see gas dripping down off the edge of the tank right below the new sending unit. When I parked it, there was 3/4 of a tank. It is now down close to a third of a tank. It has to stop at some point when the gas reaches below the edge of the new sending unit seal right? Now, this is the first time I have changed a sending unit. I am wondering if I did something wrong. I put the gasket between the sending unit and the tank and then turned the outer ring to secure it. Should I have added some kind of gasket sealant on the gasket? Both sides? Which is gas friendly?