Antonio is right.
The #1 best thing for you to do next would be to go to your bank and tell them that you realize the check you deposited is fraudulent.
They are going to figure it out very quickly if you don't tell them. It will be better for you if you go to them first.
Also: you can "Flag as inappropriate" this job posting, if you have not already done so.
For future reference:
Even if the $2000 check they sent you was real, you would not be able to accept it or deposit it, because doing so would be a serious violation of Upwork ToS. Upwork does not allow freelancers and clients to exchange funds except through the Upwork platform.
I'm surprised to hear you were just scammed because you kudoed 2 posts in the Tips to Avoid Questionable Jobs thread in October.