Best way to conquer SC in 3 weeks?

[sabrinas.]

I have a little over 3 weeks for my GMAT and I'm terrible at solving Sentence Correction problems.
This is my weakest area in the verbal section.

Can anyone please recommend a book/course/downloadable content/strategy to improve this section in a short period of time?
(Preferably some material that does not contain unnecessary things but only what is relevant to GMAT grammar)

Thanks!

p.s. I am currently doing questions in the Official Guide.

[indiantiger]

MGMAT SC is really good. I would say read it in and out.