@Chichi6 Yes, cancelling that booking was unfortunately a big mistake. Guests are already taking a leap of faith when they book a place with no reviews, but when they see that you canceled a guest just 2 days before arrival, they won't feel confident that booking with you is going to work out.
Depending on when this occurred, it might still be possible to post a response to the automated "review" that appears as a major blemish on your profile, and explain that you made a rookie error. You can also try offering a deeper discount for the soonest available dates - even if it doesn't pull in enough money in the short term, getting a few good reviews onto the record will dramatically improve your odds of attracting full-price bookings.