HELP how do I stop making half baked songs

Hi! I have been making songs in software for like almost 2 years, and my problem is in general that I get a song idea, but somehow the idea always so half backed that when I am finished with that part of the song where the melody comes in, there is just no more room for other ideas aka I don't get any vision on how to continue with it, so I always end up just copy pasting parts which is very boring and makes my songs way too repetitive and dull. Anyone has an idea what I should do?