No, don't beat yourself up Stu - you did it just fine. The issue is that the planetarium software doesn't take the fact that the object is so close into account. If it were a normal asteroid orbiting beyond Mars the plot would have been spot on.
The first time I went on the hunt for a NEO I did exactly the same and found myself searching for the rock over a degree in the wrong direction and saw nothing of course.
The next night I had licked my wounds and found it in a few mins!
Its a real thrill to find these objects and I plan to track this one over a few hours to see if It is a variable or not. If it is irregular in shape and is tumbling, it should vary in brightness over a few minutes and that will give an indication of the nature of the asteroid as only solid rocks can spin quickly. And of course it makes a difference to know if a single rock or a hail storm of smaller rocks is going to hit you
