He doesn't have his modern knowledge because he is still a fairly low level consciousness. He can't even remember his own name or face
It was also worth mentioning that if he didn't actually have enough mana the spell would be incomplete. That could lead to two outcomes, either it would be conjured in a half-assed state or not at all while his mana would still be depleted.
A pretty good read, but the author definitely needs to get an editor to fix the grammar mistakes. The story is nice though and it reminds me of Reincarnated as a Sword.