I too have the same score in Writing assessment, but i know where i made mistakes. Try to recollect what you wrote in the test, and think over it from a third person's perspective. Think as if you are reading an article and see if it is 1) structured 2) logical 3) Informative.
Also try to think if -
1) There was excessive use of a few words (-ve point)
2) Length of the essay was appropriate (v. imp)
4) You are extermely confident of your grammar.
If you feel everything was good from your end, you may go for re-checking, otherwise start preparing for the next test, as re-checking will only be a waste of money.
I am going to write a few essays in coming days, and get feedback from my friends. If you want to be a join me, then let me know