Left lower screw doesn't want to come off
So I am in the process of fixing my Iphone 4, (verizon) and i am on step 32, I am almost done, and i unscrewed three of the four screw, but I can not get the last one to unscrew no matter how many times i twist it. WHAT CAN I DO? It's the screw on the lower right side, on the button, I really want to fix my phone, please help!
4 
1 