Need Help ASAP

You'll risk ruining the entire purchase of hair if you try to bleach it. Chances are it might turn grey or violet on you.

My advice - head to the nearest Sally's and buy a weft for the event tomorrow. You can take it out when it starts to turn on ya (which probably won't take that long). Save that expensive Bohyme from possible ruin. If you haven't manipulated it or removed the tags, you may be able to return it for the right color. Granted, you won't have it in time for tomorrow but you can use it later.

If you have a small amount of hair in your stash that matches your color, use that for the top layers and install the darker Bohyme on the bottom. I'm not sure how much of a contrast this Bohyme is to your own hair or how comfortable you are with darker lowlights but sometimes these dark/light contrasting color installs look pretty darn good.

Good luck!