I chose to attend UC Davis and as times passes, i no longer want to go there. I also was accepted to UCSB but i never sent them my SIR. Now i feel like i’d be happier at ucsb and i dont know what to do. Is there anyway i can still attend UCSB?
I was in a similar situation before. It’s unlikely but you can call admissions and ask. Sometimes they make exceptions (usually earlier rather than later).
Also, you might be going through a FOMO phase. Both schools are great. Is there a reason you’ve changed your mind from UC Davis to UCSB? Do you still feel conflicted between the two or have you made up your mind that you’d 100% rather go to UCSB?
@cloud7 i do think some of it is FOMO. Four years is a long time and I just want to be happy. I felt like i’d have more opportunities at davis but after talking to people and trying to find roommates i feel like i dont connect with many of them. UCSB would also be a big change and i feel like i’d grow more. Davis is only 1hr away and ucsb is 5 hours away. I was really worried that ucsb wouldnt have internship opportunities and Davis has the capital right here. But I dont want to be bored and thinking about what if i chose ucsb for four entire years 
you can call and ask but, my guess is that you are committed. I’d add that there’s no shortage of fun to be had on and around the UCD campus. Join clubs, maybe a frat/sorority, go to football games, and really engage in the campus culture. If you get bored, it will be your own fault.
Go Aggies!