Does mortal sin always constitute going to hell?

Hello there. I have been confused on this for quite some time.
I basically don’t know if in a case where I were to commit a mortal sin, and subsequently die, would I be damned to hell for sure, no questions asked?
Like if I were to masturbate one time OR miss mass with no good reason OR have sex out of wedlock one time (as examples), and suddenly died, would any of such things be grounds for eternal damnation?
Also does amount of times done change anything or is it just the fact that I committed a mortal sin the main issue?

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