When did you buy the game? If you did buy it with this account, then it should be in the game library of your account together with any other games you may have bought on Itch. If you used another account, or you bought the game without an account, then you should have been sent an email with a download key.
It was with this account, it was just before you released the update. It showed I had purchased it on my account but when I went to the update release page it wouldnt let me download, so I just downloaded the lastest version from my page which worked for me, I transferred my save and everything works perfectly. Sorry for the bother, and thank you for the great game! I look forward to more works in the future!