hello & welcome
don't worry you will get relief very soon.
as you are giving history that RCT is completed today only and after that its causing pain means there is something wrong periapically causing pain due to pressure.
The filling material (GP cones and sealrs) may extrude out of the root of tooth which may cause inflammation at the apex of root and pain. in such situation soft diet
& warm saline rinses may help you. Pain will subside by its own.
secondly go for an check X-ray as soon as possible to rule out the possibility of an extra canal or some remaining periapical infection.