Oleg, "should not" is a present form, so you can't use "had" with it, because "had" is used in a past context: "He made sure not to forget what he HAD said, so that he wouldn't get caught in a lie."

Many thanks Uly!
My intention was to emphasize the reference to potentially distant past, that's why I used "had".

Oleg, your instinct to use the perfect was correct, but it should be the present perfect in this case.

Many thanks again Uly! I have updated my translation accordingly - and I have also stolen your ending - hope this is OK :-)

No problem, but it's still wrong - you have to say "IN ORDER to not get caught in a lie."

Many thanks again Uly!

Oleg, in order TO NOT get... :)

Хм, что это за правила такие! :-(

это не правило, просто звучит лучше по-моему

кстати, into AN awkward situation

"don't forget what you say" doesn't work here because it doesn't refer to the things that you've already said and need to keep track of.