What is the ruling on the marriage contract and seclusion after inadvertently cursing religion and immediately repenting from it?

Insulting the religion is apostasy that expels one from the faith, and no excuse is accepted for it due to jest or मजाक, unless it occurred mistakenly on the tongue or was a slip of the tongue without intending the word.

If you uttered it unintentionally, then there is no apostasy and no issue regarding the marriage. However, if you intended the utterance, then apostasy has occurred. But as long as you repented immediately, the more correct view is that the marriage remains valid, based on the principle that valid seclusion (khalwa sahiha) is considered like consummation (dukhul) by some scholars.