How do I make these seams match up? Sewing Machines Parts and Sales in Los Angeles

I’m a beginner and I don’t even know the right terminology on what to call this. But whenever I join to ends together like in this picture:

http://i.imgur.com/v7Oyy9N.jpg

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I can’t seem to make the ends match. As you see in the pic, one side is below the other. No matter how I run it through the machine, one side is always above the other. Both sides are completely matched in length. Neither one is shorter than the other. I pin everything together and even pin the sides to that they are right on top of each other. But somehow one side gets pushed below the other.

Any tips or tricks on how to make these sides meet evenly?

I appreciate any help!