If it's cycling correctly, the front sight/gas block is probably not the culprit. I would wonder more about the rear sight at this point.
If the front sight was canted that far off, you'd probably be seeing some cycling failures from the gas port holes not lining up properly with the gas block. Short stroking, the bolt not locking back on the last round, failure to feed, etc.
And if you built the upper, you would've also likely had trouble inserting the gas tube through the barrel nut and in the receiver if it was canted too badly, and the gas key would probably be rubbing on the gas tube causing more issues when the bolt was moving forward. Like hitting the gas tube and not letting the bolt close
Another, more rare possibility, perhaps the bore was not drilled straight with the exterior of the barrel body if all else looks right.
One quick recomendation if you want to check for front sight cant, if you can put some string through the small aperture rear sight like you're threading a needle and long enough to reach the front sight, you could probably look at the string in relation to the upper receiver and handguards and judge pretty close if the front sight is straight with the rest of the gun.
I hope you get it figured out.