It looks like you're slowly getting the hang of it - good for you.
There are many such cases which might confuse the learners.
* 가지 마, 가질(가지를) 마.
* 좋지 않아, 좋진(좋지는) 않다.
* 잊어버리기 쉬워, 잊어버리긴(잊어버리기는) 쉬워.
There seems to be no end of these cases where a single 받침(end consonant) changes the meaning of a sentence. It is one of the difficulties in learning Korean, I suppose :-)