You submitted it correctly, but it was too late to enter the contest by the time you entered.

It still qualifies as on time as a required assignment for the October Prep Challenge. It just doesn't qualify as an entry to this week's contest round (these are separate contests). In order to qualify for the contest round, you need to get the contest entry posted and logged before 12 noon WDC time on Sunday.
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Regards,
Eric Fretheim
Assistant Prep Leader, 2015 October NaNoWriMo Prep Challenge

"It is perfectly okay to write garbage-- as long as you edit brilliantly." ~C.J. Cherryh

“No, writing 50,000 words in a month is normal. You are not crazy. This is not insane.” ~Teri Brown