Hi @Tamar19
Sounds like you have let your listing go live before you are ready. Do have a read of Airbnb's Help Centre and the useful guides here. They are a real help in getting you up to speed on how things work.
Please turn off Instant Book so you can decide which guests to host on a case by case basis until you are more familiar with how things work
@Birdie mentioned Airbnb let her cancel because of a family emergency so probably did this under extenuating circumstances. Normally they won't do this, if it is not extenuating circumstances - for example if you didn't keep your calendar up to date.
If at all possible I would try and host this guest. So for example, if you aren't going to be around, do you have a friend that could check this guest in for you? If this isn't possible call Airbbb (all the ways of contacting them are at the top of this forum) and see if they can help but be prepared to be fined and have your dates blocked.