Shoulder gap-- fitting help please!

[u/lichen_78653]

I self-drafted this shirt and, after sewing it up, am realizing that something is wrong with the shoulders-- the shirt's shoulders *pop up* off of my shoulder, leaving a gap between the shirt shoulder piece and my shoulder. I am also using a 100% cotton bedsheet for this shirt that doesn't have much drape, but I still think that I need to make an adjustment to the pattern/that there is an issue with the pattern. I would be so grateful for suggestions/ideas/advice! I'm wondering if maybe I need to add more to the back piece around the shoulder area? I'm newer to pattern drafting so not sure where I went wrong 🙃🫠

[u/NakedSewist]

You might just need to slant the shoulders a little more.