Was I wrong to my puppy?

I have a beagle puppy. I just love her so much. I am not hard on her at all. I let her get away with everything. However, the other night she was misbehaving rather badly so finally I placed her on my lap and gave her two swats on the backside with my hand. It wasn't even hard enough to hurt. She is a very smart dog, and she knew she was being disciplined and that I was upset with her. And she started behaving better. Still, I love her so much, and I hate to discipline her.