Why do I stutter more in Spanish more than outside of class?

Why do I stutter more in Spanish more than outside of class? I am taking a Spanish class, where i need to speak Spanish. I understand Spanish, but i don't speak it well nd I stutter multiple times. Then i never get the words out. Makes it much harder to speak, to the point where I am not sure I want to say anything. I stutter in class more than outside of class. However when I talk to my friend or friends in Spanish, i don't stutter at all. I don't get this why is this? Does anyone else experience this too? If so, how do I deal with it? I feel stuck with this. Please let me know.