In all the vastness of the universe, “we were the first” is a stupendously implausible hypothesis compared to “we were the only”.
However, there exists or has existed one planet with the first civilization ever.
Even if each of those events were actually inevitable, planet size, radiation received from host star, exact chemical makeup of atmosphere/oceans and any number of other variables could affect the time scale for a planet to fruit.
If it is difficult for civilizations to develop, then our existence is so implausible already that being the first is not such a leap.
There are a 100 billion galaxies. I'm ready to guess each has at least a few planets theoretically capable to sustain life for long enough.