I bought this for my 55" tv and it works great. It had solid reviews on Amazon and I think you would be fine with this
Do you have a link to the mount specs? Looks small for a 55" capatible mount.
Edit: I'd recommend you get a heavier duty one like this
The standard things most people have, like this one which I used inside: https://amazon.com/gp/product/B00SFSBHW4
It's painted black, right? Would that work outside too?
Flat screen TV mounting holes can be all over the place.
Future proof: https://www.amazon.com/gp/product/B00SFSBHW4/
How much does your TV weigh? It should be fine even on one stud tbh. I have something like this: https://www.amazon.com/gp/product/B00SFSBHW4/ref=oh_aui_search_detailpage?ie=UTF8&psc=1 and it's holding up a 50lb tv just fine.
It may be better to use a single stud mount centered on the stud like this: https://www.amazon.com/Mounting-Dream-Articulating-400x400mm-Rotation/dp/B00SFSBHW4/ref=sr_1_2?ie=UTF8&qid=1479394092&sr=8-2&keywords=one+stud+wall+mount