Well, that's strange. I haven't get into this, but I always install on expert mode. Sometimes it gives an alert if you have uefi, so it's best be alert on this part.
You can try reboot with your install media and try to repair the grub install. Maybe this Debian Wiki articlle can help you.
Good luck!

Brasilia, Brasil, born and raised since 1979

@georgetakei
As they say around here " all punishment for a cuckold is too little". :D

me too. very happy with it, and 10 bucks for the paid version is pretty inexpensive.