There is nothing like competing to improve your dancing. I too started taking lessons with my husband for social dancing, but then wanted to improve beyond that. So I signed up for a competition shortly after I started taking private lessons with my instructor. It was the best thing I ever did! I was a nervous wreck at first, and very frustrated, like you, but I quickly found out that even the best dancers miss steps from time to time or blank out and make mistakes. If you love what you're doing, and you're learning the proper technique, it will show through and you'll do just fine. Having a goal will get you motivated to do so much better. When you get out on the floor, have confidence in your training, perform your heart out and have fun!
I still dance socially with my husband, and take classes with him from time to time, and it's great. But preparing for a showcase or a competition is what I really love. It takes time and hard work to feel competent, and I'm only one year into it, but it's such good exercise and so much fun, I can't imagine life without dancing.
Best of luck to you!! Stick with it!