The yellow ribbon means you got 3/4 choices correct.
The endings aren't that much different from each other (I only had 6 minutes at that point.) there's one for winner, one for zero correct choices, and one for any honorable mention. Pretty much all that changes is Karin and Garu's reaction to your cake, and if you get losercake, Erika says something to Ren.
90 minutes is not much time at all! I had more "choices" planned originally. There was more of a dating sim element, more interaction with the characters, and you got to choose who you wanted to share your cake with in the end.
(Also, since someone asked: Akuma Kira Erika isn't a real show.)