You didn't assign your converted data frame to a variable name, so no changes were actually made to Data. I suspect that's why you're getting the same warning.
I can't go any further without first making sure that you've seen our community guidelines on asking questions related to class assignments: FAQ: Homework Policy. The most important parts are:
- Please don't post verbatim text from your assignment
- Please clearly state when a question you post here is related to an assignment
Can you please edit the post where you included verbatim assignment text, changing it to a paraphrase, instead? It's definitely useful to understand what you're trying to do (that's part of the reason for the second rule!), but it needs to be written in your own words.