Don't stress about blocking in class. You're going to block...so what? By all means continue to work on fluency as you desire. But don't sit unrealistic expectations. You're a stutterer. You're going to continue to stutter for a while. You may become 100% fluent at some point. But in the meantime, You're going to have blocks. Nothing to be ashamed of. stressing over it's only going to make it worse.