Way to late for me to be doing math, obviously. But that verse does say that if a person comes to you and asks for forgiveness you are to forgive him 7 times 70. So that verse is saying they must ask. But there are instances all through the Bible of people being forgiven without asking.
On another note, I believe the “turning the other cheek” doesn’t mean to let the guy slap you again. I believe it means we are to walk away from the fight.
Or it could be in the context of allowing someone who asks for a second chance that chance, rather than invoking the “fool me once” mantra.
In context, turning the other cheek means offering the other as well. And, “If someone takes your coat, do not withhold your shirt from them”. But that’s not the same as allowing sin to happen. If these little acts of self-sacrifice are lost like pearls cast before swine then again, what good are they?