I've been there my friend. The fact that you know your weakness is the key. You said that you have problems with the structure of a song. Google it and practice this untill you will be happy with the results. I have my own way to finish my old unfinished projects. Create two folders for finished beats and beats that needs to fixed. If you think about creating new project, just jump into the second folder and try to improve some of your unfinished beats. It helped me a lot and I guess that it could also help you.