Thanks a lot for playing and rating my game!
I agree it can be annoying to wait long for retrying. Actually, you can triple tap or long press R for a quick retry, but I forgot to include that in the help page.
For level 4, the only reason that you feel its RNG dependent is that probably your solution is not the intended one. The intended solution is to first flush the duck into the pit with large water, then after all flow settled you start to burn the plank. The order of these operations is important.