Pay attention to the table at the top which explains the
different phases of the activity.
See if there's a green check mark next to the phrase
"Submit your work" in the "Submission phase" section.
If yes, you have successfully submitted your work. You can
click the "Submit your work" link to see your submission, and
you can edit it before the deadline if you'd like to. If
you don't see a green check mark next to "Submit your work",
you have not submitted your work.
If you have uploaded a document as part of your submission,
make sure that it is in a proper file format (eg, an MS Word
file). It is always a good idea to download what you have
submitted and then to open it to check (a) whether the file opens
and (b) if it has the right contents.