you might be right, but "것" has more of a light "-ts" sound in it more than an "-ng" tone. if you listen closely, you can hear people pronouncing the ending syllable of 것 with the ending sound that follows in the word projec[ts], and eventually, over practice and time, you might find yourself dropping the "s" sound in "-ts", which will bring less of a foreigner vibe when you speak. hope this helped!
What helped me from my various studies from years ago is that (forgive me I don't have korean on my phone's keyboard rn) the difference between ku and cheo is that cheo is like old english "over yonder". It's just further away than ku. What also helps me that duolingo doesn't really mention is that "geot" you could say is like of like "thing" so when you see i-geot it's like saying "this thing". For those of you like me who have to know every little thing about every little piece