Depending on the requirements of the contest, your diary might not qualify - for example, if you try to join a contest Seedsman is running and you're not growing a Seedsman strain, your diary won't qualify. If the contest requires a harvest and you haven't harvested anything yet, your diary won't qualify. Just read the requirements of each contest and figure out whether or not you'll qualify... You could, for example, enter the Photo of the Month (since you've got photos) or Newbie of the Month (you can qualify for this even if you've become an apprentice) or (I think) Diary of the Month (but this might require a harvest)... Grower of the Month is a horrible HORRIBLE contest that you are entered in automatically if you answer someone's question that has been attached to a diary and they choose your answer as the one they're going with... I say it's horrible because there's a lot of cheating and it's a tough one to get through EMOTIONALLY... just read the comments below that contest... awful...
But if you really want to enter a contest, just make sure you're picking one you qualify for! Good luck!