Sorry for the delay:
I'll check with kha - to see if there was an issue. Can you check again and see if this works, and if not can you please provide some screenshots of the steps and issue as it happens?
As far as the (builtin data source with your username) - I assume you mean your own personal file space data area where you can upload data files to. When creating an app with data - it represents the path like this:
FROM [lib://mtarallo/2017_video_index.xlsx] (ooxml, embedded labels, table is Videos);
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Carlos - Apologies for this inconvenience, can you try re-uploading your data source files and try again?
If you still have an issue seeing your data files after that i will open a case with Cloud Operations for further investigation.