@Eugenia27....It would possibly be wise for you to also change your booking calendar to 'All future dates' from the present 6 months because some hosts are experiencing a problem where the system will automatically remove blocked dates as the rolling calendar window comes to them. This does not appear to be a routine occurence but, a significant number of posts suggest that this is happening, and prospective guests are instant booking dates you thought you had blocked!
What @Steve143 says is absolutely correct in setting start and end dates saves a lot of manual work and rechecking, but some hosts are reporting that the system appears to be overiding your settings! A bit of confirmation or advice from Airbnb regarding this, or at least an acknowledgement that it is happening would be nice, but not likely to be offered!
So, by selecting all future dates the rolling booking calendar does not come into effect and when you get nearer the blocked period of time so that that rolling window only takes effect after your blocked period has ended, you can go back to setting your 6 month window.
It would also be prudent Eugenia to set 'instant book' only to accept guests who you approve, rather than who meet verification standards! This may help to inhibit incidental booking!
Cheers.....Rob