There can be several reasons for distortion at your input.
What is your source (pulse) generated from, can you look at the pulse on a scope without the op amp connected, is the pulse distorted.
How have you built the circuit, have you used long connecting wires for your breadboard and do you have a good ground connection.
The op-amp itself could be a problem, the relatively slow slew rate of the op-amp would indicate that you will get a fair bit of distortion through the amp, especially at such a small signal level.
The rise time of your pulse would indicate that you would need an absolute minimum bandwidth of a couple of meg to minimise distortion. The datasheet shows that at a gain of 12 the gain for this op amp is around about 2Meg so reducing the gain may give you a bit less distortion.