Discard Elf during fight & Yuppie Water

[DRaider_GR]

Hi there. I'm new in Munchkin world with my group, we've played 4 games so far and we've loved it. I've spent some hours reading rulings about card combinations, but came across a situation i am not sure what happens.

I'm an Elf of level 9 and fighting a level 4 Leperchaun with +5 against Elves so we are tied with 9 and losing.
I play Yuppie Water which gives Elves +2 and a thief successfully backstabs me -2. (9-9, losing)
I play +3 Freezing Explosive Potion and another thief fails to backstab me, then plays +10 Humongous to monster. (12-19, losing)
I play +5 Magic Missile & -5 Baby to monster (17-14), they answer with +5 Intelligent monster. (17-19, losing)
I say I don't want to be an Elf anymore and so monster goes -5. (17?-14)
Last move, they play +2 Nasty-Tasting Sports Drink to monster. (17?-16)

And here comes my question. Normally if you have a Race/Class related item in Use, you turn it sideways when you discard your Race/Class, so you only Carry it. But what happens with Usable Once Items like Yuppie Water I used in fight above. Does the +2 still counts to my total or when i discard the Elf race i must not count it anymore?
The other players didn't notice that and because it was a late game I said nothing to win and finish it. But because we are new gamers I would like to know and inform them of what happens, next time.