You're absolutely right. You could assert that and believe yourself to be right. The only thing is is that there is no evidence for that god. What I'm getting at is historical evidence. Sure you could say your god created everything but there is no grounds to base it on. In my case I have the Bible with which to argue for the existence of my god. And, I know many disagree but I fail to see why, the Bible has never been proven historically inaccurate. In fact, the more we study history and dig up new artifacts, which occurs almost daily in Israel, the more the Bible can be viewed as being historically sound.
Here's an article on how the Bible can actually be trusted and is historically accurate.
http://www.gotquestions.org/Bible-mythology.html
But since there are other religions with their own holy books how can we know that there is only one true religion? This article addresses that question very well.
http://www.gotquestions.org/correct-religion.html
And if you're interested to learn more that question check out Jesus Among Other gods by Ravi Zacharias.