What Whiteclaws said, but also it's only going in small increments because the event is only running for a single tick .. the tick of which you click the mouse button.
What you'll need is another variable, call it "TargetAngle" or something
+On click
-> set TargetAngle to -30
+Compare two values: LayerAngle(0) is not equal to TargetAngle
+Compare two values: is anglediff(LayerAngle(0),TargetAngle) Greater than 1
?->set LayerAngle(0) to Anglelerp(LayerAngle(0) , TargetAngle , dt*0.5)
+Compare two values: is anglediff(LayerAngle(0) , TargetAngle) Less or equal to 1
?->set LayerAngle(0) to TargetAngle
The reason for the last event is so it stops the lerping once it's too close to really recognise the change.