If you compare to Warlock's Curse, the curse explicitly states that the warlock must hit. Hunter's Quarry has no such specification. It simply says you deal extra damage once per round. Some might take the term "extra damage" to mean that there has to be some existing damage (ie. a successful hit) to which the Hunter's Quarry damage can be considered "extra." But such an interpretation is not explicit. 1d6 damage on top of no damage is still "extra damage."
Rules as written = you don't have to hit.
Rules as intended (IMO) = you have to hit, basically functionally equivalent to Warlock's Curse.
I expect errata on this, and in my games my players have to hit.
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edit: oh, I guess there WAS errata on this. excellent.