I can understand the confidence thing mate, but that will come in time, the more you get used to the job.
Good thing tho i think, if your slightly unsure, you seem to double and treble check things, and take a little longer, Obviousl at your own expence. ( In my case neway)
I recently done a job ( my first proper customer) and i had to remove two sink taps and some pipework going to the sink, aswell as some various unused pipework that was for a washing machien.. The pipework was in Steel, and i have had no training at all. Took me 2 hours to cut threw these pipes. The other issue i had was not knowing how to connect copper to steel.
Now knowing the options i had, its funny actually, as the customer wanted speedfit to the taps, This is what they had.
These things are like driving. You spend alot of time learning, and even pass your test, but the game only realy begins the first time you go out on your own, and for many years after!