One tip when putting in the last brick, or key brick. Butter up the bricks either side with only a very thin smear of mortar, and butter up both sides of the key brick. The thin smear on both sides stops the mortar on the key brick being pushed up as you press the key brick down. If you make the mortar a slight wedge shape on both faces as you push it home excess mortar doesn't get trapped between the brick and arch centre. This stops the brick going down properly. It's important not to allow any mortar to get under the brick. If the joints aren't filled properly, it's easy to get more mortar in with a tuck jointer or finger trowel. Make sure it's well compressed in.
I'm sure you'll work out and look forward to the photos.
