hi!! idk if u got it already but here r the steps to get that ending :3
1. i'll go see if she's okay.
2. yeah i... could show up for a little bit.
3. leave it.
4. wear something more party like.
5. knock on the door.
6. where is everyone?
and from there it doesn't really matter what you choose (only the dialogue changes depending on your choices and some cgs/memories), you'll get the ending you're looking for <3
ps: idk if it's bugged or it actually matters but i recommend choosing "only because you're cute" on the last choice bc choosing "i'll stay" won't register the ending for some reason?? like it won't show up on ur endings, idk if it only happens to me or if it's intentional but yeah ^^' hope this helps!!!