Don't try to make them fit the bumper first. Align them first, then check the gaps. If the gaps are worse than original, then tweak it A LITTLE bit, realign the headlights, and check again.
'99 Camaro, Mystic Teal Metallic, cammed L36, A4 - a little faster than you may think
'07 Silverado LT Z71, Blue Granite Metallic, Vortec 5.3L, 4x4 - Cargo hauler, daily driver