Well then I can't be too sure what's going wrong here if you are indeed playing the game from the absolute beginning without loading into chapter 1 (which looks identical to starting a new game btw, except it doesn't save the choices you make)
All I can say is make sure you go through the whole skip dialogue thing (it really saves time to tweak the speed to the max in the settings) in 1 sitting ideally without saving in between and reloading your file (not sure if this'll help but its what I do) and click on the correct choices, which for your reference is below and copy pasted off one of my other comments in case you've somehow been clicking wrong (though highly unlikely)
Otter Tale Choices: Resulting Ending:
Marlo Sex + Undies Off + Top Oyster Marlo
Marlo Sex + Undies Off + Bottom Oyster Ollie
Marlo Sex + Undies On + Top Oyster Marlo
Marlo Sex + Undies On + Bottom Oyster Marlo
No Sex + Undies Off + Top Oyster Ollie
No Sex + Undies Off + Bottom Oyster Ollie
No Sex + Undies On + Top Oyster Marlo
No Sex + Undies On + Bottom Oyster Ollie
Extra Notes: Only works if you play from the start for those who plan to complete the game fully. Doesn't work by loading saves at decision checkpoints.
Winning/Losing/Quitting the BBBot Battle doesn't affect the outcome of the choice you've picked or so I believe. So its the thought that counts I suppose.
If this still doesn't work I really dont know how I can help anymore lol