Help: for B2 petition withdraw, Thanks

I am currently under H1-B status. I filed a B2 petition several days ago. USCIS hasn't cashed my check yet, I didn't have the receipt notice either. Now I want to withdrawal the petition. Can I just cancel the check, and then the case automatically be denied? Or I have to wait for the receipt and send a withdrawal letter with the copy of the notice?

Thank very much in advance for your help.