u sure or not got same problem as mine?

i prefer something that is not sticky or leave residue when u take it off,
cos later if problem arise, (only those problem that can claim lah) still can remove and send for warranty 

take a piece or rubber or something that will not turn dusty over some period of time, (cos its too near the cam lens, dust is biggest enemy)

if u need, just cut the small o ring u got into two, and place it, at the left and right of the lens, of of u got four pieces, can put at all four sides..

since the rubber is not glued, u need to put on back cover with the phone screen face down.
thickness is vary, maybe ur phone needs something thinner/thicker than mine.

but please, not too thick, cos it will disconnect the flash module from board circuit