A couple of corrections. It will take 40,000 reputation to hit Champion
So you need to have done more than hit 12K each week. You need to maximize your reputation gain by using an artifact quality token at 12970. That puts you at 13410 rep for a week. Persons who have done that or close will make Champion next week.
Folks if you use 14 Green and 13 Blue tokens, that will put you at 11970 reputation and the 13410 if you thereafter use a purple. So maximize this week and next if you haven't already.
Actually if you haven't already there's not a whole lot of point to worrying about completely maximizing it. You only hit 40k in three weeks if you did it for all three, if you were at say 12600ish from week 1 (i.e. used blue instead of purple at the end) you'll come up about 400 rep short.