I try to figure out the structure of this sentence. but I'm somehow confuse with it

what I got is this

忘れちゃうと　いけないから、　in order to not forget

メモしといたのに　although noted it already

そのメモをなくしちゃった　that note is gone (lost it)

(If I got it right) it seem make sense to me but in grammar first two sentence is strange.

is it like this? ... although I noted it already (in order not to forget) but I lost it.