Failed quest

[BBsen]

I managed to reach nameless island and started the quest vegitarian Vampire, but I wasn't strong enough the defeat anything on that island yet, I didn't fight that vampire when I reach his house at hill top... but somehow it shows quest failed on quest list now.

is there anyway I can still complete it if I defeat the vampire , or I need to go back to old save and play again? I spent about 3-4 hours on other islands and got some pretty good items.... I prefer not to replay them

Thanks