Too nervous to speak: How to simulate a real conversation?

I can read and understand basic Arabic sentences, but my brain completely freezes the moment I try to form a response to a native speaker. I know I just need to get the reps in, so I've been experimenting with Chickytutor.com to simulate low-pressure roleplays. Is it better to correct my grammar mid-sentence, or should I prioritize flow and naturalness to build my confidence?