Not quite yet. Causing the enemy to concentrate and fortify to protect something they value is a prerequisite to mass bombing attacks. The Kurds closing in on Raqqa is the ground-based threat that ISIS cannot maneuver away from to conserve its forces. Having declared it their capital, they must stay and must defend. So let ISIS summon reinforcements and dig their trench lines.
Handled properly, Raqqa will act as a magnet sucking in more and mores ISIS fighters and concentrating them where they cannot avoid being destroyed by fire; especially by bombardment from the air. This will have to be very carefully managed and adequate Kurdish forces assigned.
The key is to maintain a constant and credible threat to the city but not slam the door on their ingress until the city is filled with ISIS. Then you must ensure the door stays shut so they cannot escape or the siege of Raqqa is lifted by a relief force.
Then bomb them, barrage them with artillery and rockets, starve them, and finally conduct a very thorough and very merciless clearing operation. ISIS will certainly deserve every bad thing that happens to them.