its trial and error i have under charged on a few and kick myself it takes a lot longer than you think and still dont know what to charge but i keep doing them until i can come up with an answer
that doesnt really help sorry
Sure it helps. It lets me know that I'm not the only one who has this sort of problem.
Being a newbie, everything takes longer than I think it should. But I can't charge for the actual time or I'd be charging £50 for a small bungalow!
I guess I'll do exactly the same as you ... get there in the end.
BTW, the technique is properly called "trial and improvement." rather than trial and error. Trial and error implies that you don't really learn from the trial.
The idea is that you make a trial and probably get it wrong to some degree. Ask yourself how you got it wrong and what you need to do to improve it next time.
The improvements to make in this sort of case may be:
1 - work faster whilst maintaining quality
2 - charge more to reflect the time taken
3 - work faster AND charge more.