Is this a valid sentence?
"I ain't no match for you!". I want to imply that I don't deserve her.
In (very) informal English, it is a valid sentence to my mind at least.
However, to me it does not mean what you intend it to. To say that you "ain't no match" for someone makes it sound as though they are better than you at some activity (a game, a fight, etc.).
If you really want to use ain't, then the sentence you need would be something like "I ain't worthy of you!".