I don't understand why you are not following the good advice given here.
I too chime in to tell you to be honest with the bank. Go talk with your branch manager in private. Tell him what you told us here and of having a concern that this check might not be legit. This way you kind of enlist the bank to be your ally in finding out if the check is real or not. If it's real, good for you. If it's not, you won't have the money, but you will have something far more valuable, - YOUR INTEGRITY AND HONESTY.
Once I was given a LARGE bill too much at the bank. As soon as I found out, I called the teller at the bank and told her of it and drove back to town to return the money. It saved the teller from big trouble and I felt good to have done the right thing....
If the check you got is legit, you've gained the money. If it's not and you are not honest with the bank, you've lost your integrity. (your integrity and honesty should be more important than your immediate life.)
-I sympathize with you needing money because you are not working, but consider this to be a test (for yourself) to see what you're made of. Seek the right answer, it's within you.
Best wishes and kind thoughts, -Spinner