garnier olia dark platnum brown darker than dark brown

I googled this and have then read some horrible things about at home hair dyes, severe allergic reactions, deaths and quite a few reviews about hair snapping specifically with the Garnier Olia. I did a patch test and all has seemed fine, no stinging no burning no itchiness except the area I did the patch on feels a little on the dry side. My natural hair colour is a dark brown so I have dark brown roots and blonde ends and wanted to just go all brunette. Usually I would go to a hairdresser but since they are all shut during lockdown I thought I would try it myself. So two days ago I went and bought myself some hair dye, my friend recommended the Garnier Olia in shade 5.0 Brown so I went ahead and purchased for myself. I am now petrified to dye my hair at home and was wondering if anyone has had a bad/good experience with this hair dye/ shade or if they think I shouldn’t dye it because of the patch test making my skin a little dry? Is that an allergic reaction? Any advice would would be greatly appreciated.

Garnier olia dark platnum brown darker than dark brown