Thats why you keep your notebook backed up, very easy on a mac with timemachine, automatic backup at least once an hour. Another good idea would be something like mobile.me or dropbox.
Anyway, the advice from coradine is to put in a flight for each type of flying you want to keep separate and put in the total of all hours done that way in that one flight iirc. Apart from that ask in their support forum, very helpful replys pretty soon after every question. Or just browse their website, a lot of usefull info there as well.