You can contact universities on your list and ask if they still accept the application. Most of them would say no because it is too late as you realized. But try to contact the admission office ASAP.
Some good universities like University of Pittsburgh or Penn State have rolling admission system.
The best advise that I can give you at this point for you is to find universities that have rolling admission system and apply ASAP.
I suggest you do a search on “colleges with late application deadlines”. I just did it, and there are a number of US schools with March 15 deadlines. There are also a bunch with March 1 or 2 deadlines, so if your application is ready to go, you might be able to ask for an extra couple of days. It may be helpful to find a couple of schools that you like with March deadlines and then contact them individually. This year, many schools seem to be willing to stretch their deadlines a bit.
If you are open to a UK school, it seems there is a way to make late applications to some schools there (UCAS Extra and UCAS Clearing). The UK schools decided on a department by department basis and will often decide based on your final IB scores plus a personal statement.
Of course, your situation is not optimal. Why do you need to start in September? If you could push it out a bit, maybe you can also research schools that accept freshman for the spring semester.
At the beginning of May there will be a list of colleges published that didn’t fill all their open places. You’ll be able to find a reprint on this site. There will likely be no financial aid left, however. There are often some good schools on the list, though.
Do you have a TOEFL score already? That will be a requirement to apply to a US college as an international student.