Apple iPhone 4 - Screws stripped at bottom when replacing back cover?

So I bought a back plate with screws and it also came with the one tool, the screwdriver. I was trying to unscrew the screws with the screwdriver but to no avail. The screws had 5 points on them so they were the pentalobular screws and so is the screwdriver. Now, they've been stripped and worn out badly. They're basically circles.

I've tried the super-glue method but it didn't work. My sister tried it on her phone but they worked just fine for her.

Any ideas on how to remove the stripped/worn out screws?