Hey @MrPanda,
It is great to hear that you have passed the assignment. If you followed through the steps in the link provided by Saif, there was a step that asked you to rename your current notebook, so the system is able to get you a new one. Note that if the notebook’s name wasn’t changed, then the system will not replace your notebook with a new one because that will essentially erase your exisiting notebook (and existing work) which is very unfavourable. Changing the name allows the system to get you a new copy with the original name, and at the same time, your current notebook was saved with a different name. Two notebooks (one new, one old) with two different names. 
Just for other learners who read this, even though it had worked for @MrPanda which I am happy to hear, there is no need to download, change, and upload. If you need a fresh copy, just follow all the steps provided in Saif’s link or here.
Cheers,
Raymond