if you are in a meeting and you are arguing in support of a particular position, but you see that everyone else is against you, you could back down so that the meeting can proceed. ------ back down.
Echarse para atras, to stop holding to that position, to withdraw from a position, opinion, or proposal. retroceder, echar hacia atras.
If you promised to help your friend move to a new apartment, but then you call her later and say you're not available, then you are backing out... back out.
Write up is used for taking a larger amount of information and putting it into a formal report that will probably be published or distributed to other people... write up.