Yes. Barring certain abilities that reduce the magnitude of a ritual or let you substitute something in place of crystal mana, a mastered ritual requires half its magnitude (rounding up) in mana crystals, whilst an un-mastered one requires its full magnitude.
The calculation here is:
I need to hit mag 3.
Assuming I have at least 2 ranks of lore, and the ritual mastered.
I contribute my maximum 2 mana towards the ritual. As I have the ritual mastered, each mana counts for 2 magnitude. Therefore I hit magnitude 4. As this is at least the desired magnitude, I can cast it.
If I only had 1 rank of lore, I would have to get another rank - such as from a regio or a potion - in order to be able to contribute more than 1 mana.
Supposing I had 2 ranks but didn’t have the ritual mastered:
I contribute my maximum 2 mana towards the ritual. As I don’t have it mastered, each mana only counts for 1 magnitude. So I only hit magnitude 2 - I can’t cast this ritual.
Again, if I had a boost to my lore from a regio, potion or otherwise, I could contribute 3 mana, which would let me hit magnitude 3.