First issue: I'm guessing you need to change the incorrect answer to None instead of -100. None means you get no credit. -100 means not only do you not get credit but you lose points. So, if a user marks all three correct answers but also the incorrect, they get 0 points. With it set to None, they will get credit for the correct answers.
Hmmm...maybe Totara? You might check with whomever you bought the add on from...You should be able to set a grade to pass in the grade book but if there are global settings from a third party plugin, it may not matter...