Glad that you liked our game.
There are 3 levels.
You just have to backtrack back to main menu via home button or ESC
then select a new level with left/right.
(On mobile there is a bug that prevents pressing left on some levels, it's fixed in dev version)
The last star is defined via the combined score.
<0.5 Bronze
<0.3 Silver
<0.1 Gold
As your combined time difference was 0.191 it remains as silver.