Noo!! Don’t be that harsh with yourself!
You are learning and that is MUCH MORE than a lot other people is willing to do 
Lets try to find out the problem!
First of all, I think you are not removing the previous widget when you open a new one. Fpr example, you should remove “Main Menu” when you open “Nessy” before adding it to the viewport. Something like this:
Another thing I can see in your screenshots is that you are still trying to play and stop music from your Main Menu. You don’t need to do that anymore, as you can control that from your Music Manager usgin the corresponding functions. I highly recommend you to do it in each Widget’s “Event Construct” as shown below:
You don’t need to stop the music manually, as you are already doing that inside each function on your Music Manager.
Additionally, if you wan to add fade effects to the music, you should do that inside each function in the Music Manager, not in the widgets.
Let me know if that works! And keep learning, you are doing it great