It's generally recommended if you throw up to ditch the attempt and continue trying to throw up since you don't know how lethal the dosage can be. That's why AE's are recommended as it's your #1 opponent.
I wouldn't recommend downing more since I'm unsure of higher dosages of SN can have - I assume it'll be less peaceful. In short I recommend waiting for your attempt, to my knowledge AE's are easy to come by. I recommend reading up on PPH it will do a way better job at explaining the role of AE's and how SN works for end of life use.