It seems you're trying to express that something was bound to happen, or that it was unavoidable. Here are some correct ways to express this idea:
* It was inevitable. (This is the most common and grammatically correct way to say it.)
* It was bound to happen.
* It was unavoidable.
* It was only a matter of time.
The phrase "it was inevitably" is incorrect because "inevitably" is an adverb, and it needs a verb to modify. In the example, "it was inevitably" is missing the verb to make a complete sentence.