C-l shows that the text is wrong, first type
C-h l (
view-lossage) to see what commands you typed to produce the observed results. Then try undoing the changes step by step using
C-x u (
undo), until it gets back to a state you consider correct.
If a large portion of text appears to be missing at the beginning or end of the buffer, check for the word ‘
Narrow’ in the mode line. If it appears, the text you don’t see is probably still present, but temporarily off-limits. To make it accessible again, type
C-x n w (
widen). See Narrowing.