Nomenclature

You don't explain why you get the impression that atheism is dogmatic, but it appears that you mix terms which are not interchangeable.

• If you leave catholicism because of your dislike of any kind of enforced structure, it means you're antireligious and probably anticlericalist.
• You didn't say anything about your faith, or lack thereof. It's possible to leave catholicism or any other organized religion while still believing in some kind of god, possibly a different one than the one described in your previous religion.
• If you still have faith, you're a theist. If you don't know whether a god exists, you're agnostic. If you don't believe in god, you're an atheist. From the short description you wrote, it's not possible to determine which category you belong to.

Is atheism dogmatic?

First, atheists aren't an homogenous group. The vast majority of them is silent, sometimes for security reasons. They often have nothing more in common than simply not believing in god. A famous description is:

"Atheism is a religion like not collecting stamps is a hobby."

Some atheists are certain that there isn't any god, some will try to convince theists that they are wrong. They still don't belong to any official institution or blindly follow principles, though.

Some atheists will try to use science (e.g. Russell's teapot) to "prove" that there is no god. This might be dogmatic, but science at least has the advantage of being falsifiable. As noted by @FrankHubeny in the comments, science never considers models to be 100% correct when describing the universe: they are merely "good enough" for the time being and probably will be replaced in the future.

Finally, the "Church of the Flying Spaghetti Monster" has been created as a joke, but could be considered as dogmatic for some hardcore followers. By its own definition, though:

"the only dogma allowed in the Church of the Flying Spaghetti Monster is the rejection of dogma"