why am I not in the top 10, how can I enter one?
To make it to the top 10 list, only 'active' referrals are counted. For example, members you refer who have no forum activity will not be counted. So to answer your question, you need to refer more active members to the forum to make it to the list.
You can check your total referrals on your profile page though. The total referrals counts every referred member, not just active referrals.
I am considering making the statistics larger to perhaps the top 20. Then more members will show on the list. Any changes to the contest terms will be posted here.