Great advice on this thread, but I'm going to suggest something different.
A while back, I was a cardio machine ... I would bike hills 40+ min to class, roll hard with bigger guys for ages, then bike home. And in tournaments...I would get trashed. Trashed bad, and I could feel it that I was 20% of the fighter that I was in class.
to cut the story short, stuff happened in life that destroyed my cardio (illness, work...) and I for mat survival, I had to craft a game that would conserve my gas. Day in and day out, I was fighting to stay in positions that were less tiring, and trying to conserve gas whenever possible. I started feeling good about my game, and decided to compete again. I found that my "gas-conservative" game got me through the early part of my match ... I was no longer so dependant (physically or mentally) on having strong cardio. When I started sucking gas (due to nerves), it didn't worry me - I was used to that. I ended up winning that tournament, and things in competition have really turned around for me.
Obviously, I am not suggesting that bad Cardio is an advantage. But you can adjust your training, and craft a less-cardio dependant game that is more compatible with tournament nerves.