actually lerp(a, b, x) should have the x parameter variying, not the a parameter (it is a simple linear interpolation by defining a 0 to 100% value), it just happens that it do something else the way you (and not only you) are using it (I think this is called a geometric progression), but in your case:
-did the angle moved too slowly? (since 0.9*dt is a very low value, it will stay relatively close to Self.angle, and so self.angle won't vary that much even at the beginning), maybe a 0.5*60*dt will be more noticeable (it should be half way of it's current position 1/60 of seconds later).