Since when is sex within the bounds of marriage *carnal relations*? What is it with the Catholic mind that views sex as something wrong or dirty?
Mary simply asked the obvious question of how it was possible for her to become pregnant because she had not YET had sex, not because she never intended to.
Her never intending to affects her future, not her present. That would be a stupid question to ask if what she meant was what you say she meant.
How can I be come pregnant as I never intend to have sex with Joseph?
That's just silly.
Deliberately silly. It’s a joke to some, IMO.
"Carnal" means "of the flesh" and "relations" means between two people. Yup, sex is carnal relations as it is an activity done between two people in the flesh.
Mary simply asked the obvious question of how it was possible for her to become pregnant because she had not YET had sex
The answer to that is also obvious: by marrying Joseph and having sex with him. Every girl old enough to be engaged to be married knows that and needs not ask.
How can I be come pregnant as I never intend to have sex with Joseph?
That is exactly what Mary was asking. The answer was, God, not Joseph, will give you a child.