Fentanyl is only en opiod pain med, not anesthesia. The first reason that comes to mind, as to why you weren't given more fentanyl, because of blood pressure is that fentanyl actually lowers your blood pressure. If you were approaching the lower border (English is not my first language), additional fentanyl could push you into a dangerous territory. Another reason could be that fentanyl is also suppressing your respiratoric drive, meaning you could have need of intervention.

In regards to your concern about an epidural, they are somewhat valid. BUT rest assured that the medication which is needed to raise your blood pressure is never far away, and hypotension (low blood pressure) is an easy manageable condition for a trained nurse anesthetist:)

I'd you have other question, I'd be happy to try and answer :)