there's a few things I would check first
Measure the width of both separate pieces from underneath. They should be identical, and if one is wider that's your problem.
I suspect the angles are OK, but you may be able to see if they need to be relieved below the laminate to fit up tighter or if there is a bump on one wall that prevents it from moving closer.
The corner is "probably" not a true 90 degree. Take a framing square and see if it sits flush and fits tight inside the "L".
I suspect the pieces were made from two different lengths of post form and they are not the same width. Take the measurements with you if you go back and see what the other post form widths measure underneath to find one that will mate with at least one of yours.
It could also be that one of the backsplash boards is not at 90 degrees to the counter surface.
In order for the piece to be offset by that much, the angle would have to be off considerably and then they wouldn't mate as close as they do.....JMO.
The answer to your question will only be as detailed and specific as the question is detailed and specific. Good questions also include a sketch or a photo that illustrates your issue. (:< D)
Last edited by woodnthings; 05-12-2013 at 08:20 AM.