Don't take it hard that you failed - look on it as another chance to acquire skills. Once you are through and qualified if you come back in a year and do it again you'd be amazed at how much you still don't know, so look on riding as a continuous learning process. Controlling the bike at slow speeds without putting a foot down is a valuable skill - as is doing a U turn.
In the UK it is legal to filter through two lines of traffic - which in London is practically the only way to get anywhere. It has its risks and certainly exposes you to all sorts of dangers, but it is also an endlessly fascinating test of skill. It is totally unacceptable to touch anyone's paintwork or wing mirrors. If you do your licence is torn up in fornt of you, they rip the buttons off your leathers, no-one talks to you anymore and its a trip to the woodshed.
Personally I don't mind riding in pouring rain, but not at all if there is a chance of ice. You'll be on your ass for sure.
Good luck Simon