The paper explains it

The writing on the piece of old newspaper changes and you read:

By speaking to Karen she will be your true love for life. It is the power of the potion. She will remember always having a crush on you. She won't be a push over, drunken, pregnant slut but a good influence on you.

Karen sees that the note has turned into an ad for perfume written on newspaper with a date from 20 years ago and the vials have changed to exquisite perfume bottles. After a minute, the paper looks like an perfume ad from a newspaper to you too. Karen says that the perfume is a lovely find and tries the one in the blue bottle called Scent of Adventure. It smells great. Karen packs the old newspaper ad and the perfume back in the box and promises to let you experience each scent on future dates.

You and Karen make out for awhile until Amber crashes in. She is drunk and horny. She needs Karen to keep her from going all the way with Bobby. The girls have a buddy system to keep from getting pregnant. Karen pockets her bra and straightens up her clothing and you put your shirt back on and tighten your belt as you leave the room.

You go to find that Bobby is more wasted than Amber and has passed out. You leave a note for Bobby to take your van to your Mom's house after he is sober. You drive Amber's car to her mom's house and you and Karen help Amber to her bedroom. Karen walks you out and you both kiss each other goodnight. You then walk about a mile to your mom's house. You get a text from Joe that he and Tom escaped detection at the party. They are across the lake from the Smith place and need a ride. You text that it will have to be in the morning as you are safe but without a ride.