Not to worry. The beauty of adoption is that when it is done, it is done. For all purposes you are his mother as if he were born to you. Says so right there in the paperwork
I love that part.
He has a birth-certificate with your name on it..
I think you will need to explain the no-father listed, so they don't feel like they have to publish for a father. In that way, I'm sure the adoption will have to come up.
You can probably look in the yellow pages or online for step-parent adoption lawyers in your state.