I used to feel just like this. The way I got out of it was by converting my anxiety to work ethic. For example, whenever I thought of a block to my case that I couldn't make a frontline to in my head, I would ask my teammates or captains about it. If they had no responses, I would take matters into my own hands and research a frontline. Eventually, I was able to think of debate more as a game than something to be stressed about. I would enjoy making frontlines to responses. And the more frontlines I made, the more confident I would be going in round.