And that -- the bolded part -- is what you did wrong. When viewing the shot line, you need to use the same visual perspective you'd use when actually down on the shot. When you're standing, using binocular vision, you are using two fields of vision "merged" or blended into one cohesive picture. But, after acquiring the shot line with two eyes, if you then go down on the shot with a closed eye, you just lost 50% of your sight picture.
If you want to try this experiment, you should try acquiring the shot line (that is, the standing part) with one eye, and use that same eye going down on the shot.
Try it -- I'll bet you have more success than acquiring the shot line with two eyes, only to try to shoot it with one eye.
P.S.: if you have two healthy eyes, it's not a good idea to close one when playing pool. Reason: your mind is accustomed to having a field of vision composed from input from two eyes, so that's what you should be using. Only players with an extremely dominant eye (e.g. Earl Strickland [right eye], Ralf Souquet [left eye]) or otherwise extreme impairment in the lesser eye (e.g. Niels Feijen [90% blind in the left eye]) should try shooting pool with one eye closed, because their mind is already "used to" discarding the input from the other eye.
-Sean