The moment you start worrying, you panic and start thinking about finishing the tasks as soon as possible, regardless whether the output is half-assed or great. It might be productive but not efficient, and might cause unnecessary impediments. The more it piles up, the more you feel unease, and the voices inside your head starts getting noisy. Then, things mixed up. The more you do another thing, it mixes with the other pile of worries. It doesn’t work as a stack but rather, a clutter.
Here’s a piece of advice:
Things already happened. If you feel bad that it has started the wrong way, the most rational way is to act upon it. Your options should neither include to quit nor to recklessly finish it. What you can do is identify the impediments, both those you assume and those actual thing that have happened, and in this way you can form a strategy how you can finish the duty with mistakes reduced or at least, without worsening the situation if it is inevitable.
I know you, even everybody else, wanted things to go perfect and smoothly, but you have to consider that flaw is inevitable. And you would worry that it might affect much of it, but also it might actually not.
Regardless the simplest way to do is to be reminded what really happened, to set your mind not do it again, and to do effort, be it through rehearsing or planning, that would make things smoothly as soon as you working on it again.
Meditations, Letters, and Metaphors 