If you're only referring to/interested in the word count/quantity of your latest attempt, you could, along with the other response, perhaps also consider something like:
Je n'ai jamais autant écrit que maintenant/jusqu'à présent/de ma vie.
(please note that using "autant" probably requires "que [something]" [as in the "que maintenant" in my suggestion], to complete/balance the comparison, but IF the "que [something]" can be omitted in this case, I'd go with either "...jusqu'à présent" or "... de ma vie")
If you are concerned with the overall quality (and not just the quantity) of your latest endeavor/accomplishment, however, you could perhaps consider something like the following:
Je ne m'etais jamais avancé [aus]si loin comme écrivant [que
maintenant/qu'avec ma dernière tentative d'écrire].
(although it's probably obvious, please note that I'm not a native speaker of French, so please take my suggestions with an ample hit of salt)