Messed up battery?

Messed up battery?
I just bought my battery today. I installed it already, and for some reason I can't get that little thing in right. I saw a little white strip and I thought it wasn't suppose to be on there, so I took it off, but now it won't turn on. I might have messed it up; can someone help me out?

ANSWERS:

"Well, here's ifixit's Guide.

Can you put the white strip back on or is it now permanently off?"