Can I move a unit with shuriken flip if the enemy unit is retreat?

Yes — the move still happens.

Shuriken Flip's damage and move are separate instructions. If the enemy unit "Retreats" (returns to hand) before the spell resolves, the damage part fizzles — the unit left the board, so the targeting relationship is severed — but the move part resolves normally as long as you have a friendly unit to move (that unit is the spell's other target; Rule 359.3.e.8; FAQ #11929). The enemy unit leaving doesn't stop your unit from moving to the destination you locked in when the spell was finalized.