Spoiler installation gone wrong

[jinxor]

Hey guys,
I got a RS Spoiler and wanted to install it on my yaris....
So I painted it (not the best paint job) and tried to install it

It had two screws that needed to be drilled into the back of the yaris and put in. So I measured the screw width and drilled a 7 mm hole at the back. But the screw didnt go in....
So I took a 8mm drill bit and expanded the hole....
Now the screw is a bit loose

Can you give me a way to fix this stupidness of mine?

Also, I thought it will be fine, so I covered the top of the screw with a cap so that the screw doesnt fall out... now I cant access the screw