If you do not own Tristana as a champion, you will also receive the Tristana champion as well as the skin.
Each skin code can only be used and will only work if you have selected the correct server region for your account. If you experience any sustained difficulties, it is best to open up a ticket with the League of Legends customer support team.
If you experience any difficulties with this process it is always advised to submit a ticket with the League of Legends customer support team. Include print screen of the issue so that the issue can be resolved quicker.
Remember that skin codes can only be used once and will only work if you have selected the correct link for your respective server region.
