Vent - I feel like I’ve messed it all up

Results day was 2 days ago and I applied to another uni than my firm choice through clearing as I got in but no longer liked the course I applied for, I’m now awaiting confirmation for the clearing uni and I feel like i messed up.. now upon thinking I really regret declining my firm choice despite me not even liking the course anymore as it could’ve been changed upon enrolling or something. I just wish I could rewind time back to results day and call my firm and apply for the course I wanted through clearing - however I was too set on “I don’t like the course, I’m not going to the uni” which is so dumb. Any advice? I’ve heard that I can transfer after first year if i don’t like my clearing choice .. tbh I just wanna cry