If you're one of those 70,000, don't fret. You still have a chance to make it. Here's what you should do.
1. Wait for your University Predicted Grade (UPG).
If you didn't get in any campus, this should come in the mail, together with your rejection letter. It should look similar to our own UPCAT Score Reports here on CollegeRev, stating your percentile scores for each UPCAT subtest and a number that predicts your grade (in the 5-1 scale) in UP.
If you passed at least one campus, you probably won't get it in the mail. Call up UP and ask for the procedure for getting this if you want to get reconsidered for a different campus.
2. See the UP Campus Cut-Offs
This is why getting your UPG is important. Each campus has a cut-off, or a minimum UPG value for prospective students. If you want to be reconsidered, you at least have to meet the required cut-off of the campus you are applying to, however, be informed that UP-Diliman barely, if at all, reconsiders students for admission.
Here are the UPG cut-offs according to Academic Clinic. They are outdated, since the cut-off changes every year, but they should give a rough idea of where you should stand if you want to get in. Again, call up UP Admissions to get year-specific data.
UP Diliman: 2.2
UP Manila: 2.285-2.5
UP Baguio: 2.659
UP Tacloban: 2.7
UP Cebu: 2.7
UP Iloilo: 2.7
UP Mindanao: 2.75
UP Los Banos: 2.42-2.8
Remember that even if you meet the required campus cut-offs, you should expect to meet stiff competition for limited seats, thus admission is not a sure thing.
3. Jack up your senior year grads. Wait. Pray to whoever your deity is.
Naturally, they won't consider only your UPG in determining eligibility for reconsideration. Any appeal should ideally be backed up by solid senior year grades and school performance/discipline. These show that the student is serious and would obviously sway officials towards an admission. Don't give them any reason to reject you.
Whatever happens though, don't forget that UP isn't the be all and end all of your life. There are many schools in the Philippines of equal quality, sometimes even of superior quality, depending on the major.
Just be assured that you will eventually find your place, and that it will always be the best place for you. College is, after all, what you make of it.
Happy holidays everyone!