Got my PUP results late with a July 25 deadline! Currently enrolled in STI (SHS Alumnus) can I still secure a BSCS/BSIT

I’m a recent SHS graduate from STI, so I automatically enrolled there for college as an alumnus. I just got my PUP results on July 23, and my confirmation/enrollment deadline is already on July 25! my top choices are BS Computer Science (BSCS) or BS Information Technology (BSIT).

I have a few crucial questions:

BSCS / BSIT Slot Availability: Since my enrollment date/deadline is July 25, do I still have a realistic chance of securing a slot in CCIS for BSCS or BSIT? How fast do these quota courses fill up during enrollment?

Missing Original Documents: Since STI currently holds my original Grade 12 Report Card (Form 138) and Good Moral Certificate, I won't have them physically ready by July 25. Will PUP allow me to sign an Affidavit of Undertaking / Enrollment Waiver Form so I can secure the slot first and submit the STI documents later?

STI Withdrawal: Has anyone here successfully pulled out their credentials from STI after securing a slot in PUP? How smooth was the withdrawal process, and did you run into any issues with the STI registrar?

Any tips or past experiences would mean the world to me right now. Thank you so much!