Is the y-wing's primary attack turreted? (able to fire in 360 degrees)

Or is this only its turret secondary weapon?

Only secondary weapons. Ships that have a turret primary have it indicated on the ship base by a circular arrow around the stem base.

Thanks!

There is also the BTL-A4 Y-Wing title card. This allows you to perform both a primary and secondary attack however you can only fire within your firing arc. That is, you lose the 360 firing arc for your secondary weapon.