It's hard to know exactly what happened, of course, but the facts of the matter are that even the CCP themselves acknowledged the fact that hundreds died and all the Western journalists who were there confirmed that the PLA shot and killed hundreds of protestors.
Also, while it's true that Western journalists may have been biased, it's also certainly true that China's authoritarian and notoriously opaque government cannot be trusted to tell the truth either, especially if they were responsible for the deaths of many civilians.
While the extent of the massacre in Beijing may be contested, it seems incontrovertible that it did occur.
Furthermore, why is this event of a couple hundred casualties pushed so hard by the media as proof of China’s evilness, when Mai Lai or the 228 incident are barely talked about?
Asides from the fact that this is classic whataboutism, you are categorically wrong to suggest that the My Lai massacre is portrayed in Western media today as anything other than a horrific attack upon civilians.
It is perfectly possible to deplore both massacres, in Beijing and in Mai Lai. This is not a simple zero sum contest between China and the US where one must be the good guy and the other the bad guy.