If you don't truly use and want the Chanel I agree you should sell it to finance for something you love. If there's a chance to might regret, hold on the cf until you get the birkin. If you're happy with the purchase you can consider consigning your cf.
It sounds to me like everything fell into place for this beauty to be yours! It is indeed stunning! As long as it being pre-owned works for you, I think you should go for it!
I'd go for it! ❤