Does a PFO ever fix itself on its own?

Yes. Everyone has a patent foramen ovale when in their mother's womb. It closes on its own shortly after birth or as a child grows. This happens about 99% of the time, but there is around 1% of the population who have persistent pfo. Most of these have no sequellae.
No. Pfo stands for patent (or open) foramen ovale. The foramen ovale usually closes shortly after birth. If it remains open beyond this time, it does not close. A PFO rarely causes problems and is present in many people.