I don't want to seem rude, but what usually gets me with such cutesy sayings is that it's wholly trite and unoriginal, and why would you want that on a t-shirt you wear?
https://www.google.com/search?q=Sorry+I%E2%80%99m+late+I+did....
If someone were to show me one of these shirts, and be like, "hey, that's you!", I would kinda feel like... you don't really know who I am. You're just trying to explain something as complex as an introvert's inside life and not doing so well.
So, maybe I do feel for the author of the piece.
I feel also that (as an introvert), it's not that I don't want to hang out with my wonderful friends, it's just that there's something I want to do much, much, more, that just happens to be something I do alone. Tonight, my friends want to go dancing, and I love dancing (and I love my friends), but the weather is nice tomorrow, and riding a bike longer than anyone I know would want to is completely irresistible to me. My hobbies have become so extreme as I'm the only one that now participates in them. Anyone can go drinking and dancing. It's inclusive like that.