I have been studying Spanish on my own for about three years now. I even do volunteer work at an organization that helps hispanic residents prepare for their citizenship exams and I lead a class in Spanish. But still, I just continue to stumble over words, use the wrong words, screw up grammar tenses and so on. I think that they understand me for the most part, but I am afraid that my Spanish just sounds like crap. How can I stop making so many errors?