SLEEPY’S GUIDE TO A SUCCESSFUL CONFESSION:
Confirm your own feelings, be sure that you do genuinely like this guy and want to continue dating him.
Then, during some occasion (1 week/1 month anniversary maybe), tell him this:
“When I first texted you, I didn’t know that I liked you yet. (This makes clear from the beginning that you do like him NOW. Important starting point.)
“All I knew was that I wanted a partner, at the time. So, having heard that Hayashi had just broken up with her boyfriend, I think wanted to see if she liked me. As you know, I texted you instead. And I am so, so glad that I made that mistake.
“I really, really like you. I’ve always known you were handsome, but now that I’ve gotten to know you better, I know you’re kind, and a hard worker, and far cuter than you let on at the surface.
“So, since my first confession was unintentional, I wanted to give you a proper one. Aoi, I like you. Are you willing to be my boyfriend?”
If you aren’t confident in your ability to say all this to his face, text it. But make sure you’re available to call him/ meet him in person soon after to talk through all of the weird feelings that might come up on his end as a result.
What NOT TO DO:
Keep avoiding telling him this until he accidentally overhears part of a convo you have with your friends explaining how you accidentally texted him instead of Hayashi, assumes you’ve just been going along with it for his sake, and breaks things off between you two. That will only lead to the second half of this confession taking place after an angst-filled day or several days where you feel awkward around each other until finally you chase after him in the rain and admit everything that you could have just appended into the end of your accident confession in the first place.