I was paid 2 times after I quit my job. I reimbursed my former employer after it happened. These 2 paychecks have made me ineligible for certain credits. What can I do?

I am not eligible for the Earned Income Credit because I am now $450 over the maximum income. I was paid $766.75 twice after I quit. I notified former employer of the mistake and sent two checks back to him. What am I supposed to do?