|My first thought was that this was over-sharpened, but on closer examination, I see it's selection marks around the petals where you've masked out the background. Unfortunately, selections of any kind are not legal within the Basic Editing rule set and you may be disqualified from this challenge. Don't take it to heart though, keep entering!
By the way, if you're a paid member, this type of editing IS allowed but ONLY in challenges where Advanced Editing is used.
In any event, should you want to re-edit this for yourself, try using the magnetic lasso and set feathering to at least 10 to 20px to make the transition look smoother :)