missing card in reading.

Hello There.
I'm just learning to read the tarot. and because of time restrictions, I lay out a spread and write down the card positions before putting the cards away.

last night I laid out a celtic cross spread with the Rider Waite deck but I wrote down the same card twice. It was the one signifying the long term past influence, but I cannot remember what the correct card was. Does this matter and is the whole reading null and void?
Your advice would be most appreciated.

It's the long term past. It is over. Focus on you now.

I would tend to agree with JoyousGirl, while it would be helpful to know what the card was, there's still plenty of information to be absorbed from the rest of the reading.

I'd recommend for the future that you consider taking a picture of the spread once you've laid it out; doesn't have to be perfect, just clear enough to tell what cards you drew, so any camera will do. I just use my phone.

missing card.

Thank you both. I shall be more vigilant in future.