Vector3 to UDim2?

For one thing, UDim2's require 4 arguments (ex: {1,0,0,100}), not just two. Second of all, the position of that part won't be relative to the position of your camera. So you would have to find the position/CFrame of that person's camera relative to the part's position.

Sorry if this isn't that detailed of an answer. I didn't really expect you to understand much of it, but using my explanation, create a new question including the explanation (if you didn't understand what I just said). From there, somebody else will be able to help you (I'm too busy at the moment).