Being asmatic, please seriously think about why you are doing this before you do it. I'm not saying don't do it, but just make sure before you put yourself in that ring and risk it. If you go all out the first round and don't knock out the guy you are boxing, then what? Unless you are training, you'll be wiped and still have at least 2 rounds to go. The chances of having an asma attack will increase if you gas yourself the first round too. If you are pretty confident you can end the match in the first round then it might work out for the best. Always a risk vs reward thing
I know its difficult when your body limits the things you want to do. I've struggled with that myself. Pushing those limits past what you or other people think you can accomplish is a great thing. Just be aware of the risk you take. If you do more damage to your lungs or your body then it'll be even harder to do the things you enjoy, like martial arts.