What happened to all the antimatter created in the Big Bang?

We think that there were almost but not exactly equal amounts of anti matter and matter produced. The anti-matter was annihilated into radiation and this is what we now see as the cosmic 'fireball' radiation today. The mathematics work like this:

For every 10 billion particles of anti-matter, there were 10 billion and one particles of matter. Eventually the temperatures fell so low that the reaction could not keep re-creating the matter and anti matter after they annihilated, and so after the final era of annihilation, all of the matter and antimatter annihilated leaving behind the 20 billion photons of radiation plus the one particle left over matter. On the cosmic scale, this arithmetic was replicated over and over again to leave behind enough matter 'ash' to form stars and galaxies.

The radiation is what we now see as the fireball cosmic background radiation, and the leftover matter went into the stars and galaxies and us! We know from lab experiments that the decay processes in nature do not favor matter and antimatter equally, so this is very good reason to expect that in the early universe, matter and antimatter were present, but processes favoring matter were slightly more abundant and common.