Check the torque you applied to the external-bearings you istalled. Check with your manual of ask FSA what the correct torque is. And use a torque-wrench. Most people install these at 1/3rd to 1/2 the correct torque. And check the rest of the crankset as well.

Other than this - external-bearings are often tight at first. They will loosen up in time as you ride.