Ok buddy, take it REALLY, REALLY SLOWWW.
Serioulsy, do each note really slow for a while untill you can do that proficiently at a very slow speed. Like play the 3 on E and the 12 on G and let it ring, then go to the 5 on A and the 14 on G, let it ring, then the 5 on D and the 16 on G, let this ring, and just keep doing that.
Speed it up a teensy bit and keep going over it. Then a little faster. Then take a break (phew!)!
Then keep going faster and faster. Of course, you won't have it under your fingers in one day (I mean, unless you stayed up for 24 hrs straight playing that same thing over, and over and over

), but you should have it in not too long.
Remember, always slow it down if your not getting it.