Is there a reason to believe Owen wouldn't have seen the town if he had crossed the town line?
That wouldn't make much sense, since there's a road going right through where Storybrooke is supposed to be. Presumably, cursed Storybrooke could see the outside world, and possibly even enter it, but no one from outside could enter. Owen standing at the edge of town was done for drama, not because if he took a few steps forward, he'd have magically seen Storybrooke.
The only reason Owen and his father found Storybrooke in the first place is because they were within its boundaries when it was formed in our world.