My CPU heatsink/fan will not quite fit on my motherboard

Hello all, I have a AMD Phenom II X4 965 Black Edition CPU and I am trying to put it in my motherboard which is: ASUS Socket AM3/AMD M4A88T-M/USB3. I have it on and I can get the two square things onto their respective notches, but when I try to close down the lever I feel like I am forcing it and that it is about to break so I stop. Anyone know why this is happening? I have been fidgeting around with it and can't seem to find out why...maybe I am supposed to just force the lever down?

Thanks.