PictureBox image problem

[C# Programming]

I put the small red-green bar for a PictureBox Image and Set the SizeMode to StretchImage. However why in the PictureBox area appears white gradient in the right. I think it' s because of the small bar, because it stretches it too much. With bigger images I don' t have this problem. How can I fix it?

EDIT: Sorry for the double

http://img5.imageshack.us/img5/8015/bar45.jpg[^ (http://img5.imageshack.us/img5/8015/bar45.jpg)]

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