Add UI Panel as child of anothe UI Panel on Canvas

Hello.

I'm developing a Leader board for my game, I'm using Unity 5 and the new UI system, so I have a Canvas that contains panels, and a Prefab which is a Panel that has 3 Text inside a child panel, this is the screenshot:

I get my Leader board list from the cloud, and I want to show the player names on the Leaderboard, so I have this code that get the list, create a prefab and show the data:

 public void GetLeaderboard ()
 {
     Debug.Log ("Getting Leaderboard...");
 
     for (int i = 0; i< entries.Count; i++) {
         Destroy (entries [i]);
     }
 
     entries.Clear ();
 
     new LeaderboardDataRequest_highScoreLeaderboard ().SetEntryCount (10).Send ((response) => {
         foreach (var entry in response.Data) {
             AddLeaderboardEntry (entry.Rank.ToString (),
                                  entry.UserName.ToString (),
                                  entry.GetNumberValue ("score").ToString ());
         }
     });
 }
 
 void AddLeaderboardEntry (string userRanking, string userName, string userScore)
 {
     Debug.Log (userRanking + "-" + userName + "-" + userScore);
 
     GameObject boardEntry = (GameObject)Instantiate (availableLeaderboardEntry);
     boardEntry.transform.SetParent (leaderboardPanel.transform);
     boardEntry.transform.position = new Vector3 (50, lastLeaderboardEntryY, 0);
     lastLeaderboardEntryY -= 30;
 
     boardEntry.GetComponent<LeaderBoardEntry> ().rankString = userRanking;
     boardEntry.GetComponent<LeaderBoardEntry> ().usernameString = userName;
     boardEntry.GetComponent<LeaderBoardEntry> ().scoreString = userScore;
 }

It works perfectly, but when creating the board entries, it shows them completely out of the screen and this is the result:

The entries are set as children of the LeaderBoard Panel, as they are on the Unity Editor, if I drag them from my prefabs folder to the Hierarchy panel by hand, they are shown perfectly, I've search a lot but didn't find any help on how to fix it. Maybe some of you can give me a clue on how to do what I want.