Make sure your spine stays nuetral during the bench. Many people don't maintian that arch. You should be able to stick your hand between the bench and your lumbar.
Also be sure when doing this that you do not hyperextend the lumbar.
"When I see guys working out for cosmetic reasons, I see vanity exposing them in the worst way, as cartoon characters, billboards for imbalance and insecurity. Strength reveals itself through character." -Henry Rollins