Yes — I would revise it.

If today is indeed the garbha kalyanak of Shri Shreyansanatha, then it is not correct to say that there is no kalyanak today. In that case, today does have a kalyanak according to the Jain calendar/tradition being followed.

So the corrected statement would be:

“Today is a kalyanak day — the garbha kalyanak of Shri Shreyansanatha.”

If you want, I can also help phrase this in a more proper Jain style.