It's a default nature of the UniformGrid panel to place the first element at the first cell (Row=0, Column=0), but it also offers to set the cell position explicitly. The first cell location must be in the first row, starting the index at 0 (zero).
The following example demonstrates how you can set the first element position by assigning the FirstColumn property:
<UniformGrid Columns="4" FirstColumn="2"> <Label Content="Cell 1" Background="Yellow" /> <Label Content="Cell 2" Background="YellowGreen" /> <Label Content="Cell 3" Background="Orange" /> <Label Content="Cell 4" Background="OrangeRed" /> <Label Content="Cell 5" Background="Violet" /> <Label Content="Cell 6" Background="DeepSkyBlue" /> <Label Content="Cell 7...