My reply to someone with a related problem should clarify the mechanics: https://itch.io/t/993501/dominant-servant-stops-forcing-me-qaq
Your problem is that you only chose 1 dom outcome. Whether you can solve this in-game will depend on if you saved before the alchemy event, as the last event only responds to prior choices. If not then you can only change the outcome by editing the save file.
To edit the save file you will want to open the file with a decent text editor. Many use Sublime Text 3 or Notepad++, but generally anything better than Windows' Notepad will work. Make a backup of the file before starting as mistakes are hard to fix. The save files use JSON format, so an online JSON editor can be used but is not needed for this.
Use the Find function to locate the "decisions" list (it will have a colon and square brackets following it). Inside the list will be various text in double quotes and separated by commas. The ones related to the starting slave will start with "ss" and the ending of each will indicate the choice made. The dominant ones are ["ssweak", "ssmassageweak", "sspotionweak"]. To get the Dominant trait, exactly 2 of the choices must be from this list and "ssyandere" must not be in the list.