You should give a direct link to the competition, and then have your referral link afterwards with something like 'if you use my referral link, I'll get another entry'.
Note, this is my opinion. I'm not a mod, but in my opinion it is always better to be upfront about the links you provide to these competitions.
The referral link lead directly to the comp, which one would enter and submit in the same exact way. I didn't think that adding a ?referral to the end of the URL would negate a persons interest.
Anyway, I've removed it - Flamers will flame and I'm in no mood to defend a querystring.