Returning a dog we adopted.?

We adopted a dog today from our local shelter. I made it clear I was looking for a small dog that would get along with the pets we have and explained what kind of animals we have in our home. An older small dog and a cat. They ured me that the dog we were interested in would be great. Well we got the dog home and he does not get along at all with the other animals and has bitten my elderly mother and broken the skin when she went to pet him. The dog has snapped at me 2 times when attempting to take away something he should not have. He also has shown aggression with food and tried to bite. We do not feel comfortable at all with a dog that bites. We have friends that come over with small children and I would be afraid he would try to bite them. I thought shelters tested their dogs to make sure they were suitable for adoption. Frankly I want the $65.00 fee back I paid to adopt the dog and return him. I am in Nebraska but can not find any information if I have the right to the money back and to return him. It has been less than 24 hours. Any information or suggestions would be greatly appreciated on how to handle this situation.