Here is the only question you need to ask -- do you ultimately want to attend USNA or are you happy pursuing your commission through another source?
If you accept Foundation, you spend a year at a prep school -- generally, you get to select which one. Your family may have to pick up some of the cost, based on their ability to pay. If you complete the Foundation school successfully (academically, no major conduct issues, etc.), pass the PFT (vs. CFA), are still qualified medically, and still want to attend USNA, an appointment is essentially guaranteed. Most (if not all) Foundation students consider it a year very well spent in terms of providing add'l academic prep, learning to be away from home, learning to live w/a roommate, etc. And Foundation students have the highest retention rate at USNA of any accession source.
Or, you can pursue your career through NROTC -- an equally viable option. ROTC is a fine program and SDSU is a terrific school.
It is very unlikely, but not impossible, to be offered a direct appointment to USNA at this point. Accepting a Foundation scholarship does NOT make you less likely to get a direct appointment. Sometimes, they re-evaluate NAPS/Foundation students and decide they will get a direct appointment; however, at this late date, that is less likely than if you've received the offer much earlier.