Did you buy any ammo for the gun ?
Did you buy ammo for the gun you're firing with ?
Did you buy a force field shield to help protect you (page 48, top).
Get a high powered one, at the Shield shop.
Be sure to have cursor on attacker while you fire.
Shoot faster. And try changing your cardiogram to ACCELERATION.
Cardiogram is in Program 3 of B.O.B (page 51)