Margin in wrappanel - wpf

Question

I'm using WPF's wrappanel. the problem is that in the right side of it there's an empty space that I would like to reduce and I don't know how.
in the pic below you can see the right against the left side margin, I would like them both to be like the left one.
This is my XAML:
<Grid x:Name="root">
<Grid.ColumnDefinitions>
<ColumnDefinition Width="263*" />
<ColumnDefinition Width="240*" />
</Grid.ColumnDefinitions>
<Rectangle Fill="LightBlue"/>
<WrapPanel >
<Rectangle Margin="10" Fill="Red" Width="40" Height="40"></Rectangle>
<Rectangle Margin="10" Fill="Red" Width="40" Height="40"></Rectangle>
<Rectangle Margin="10" Fill="Red" Width="40" Height="40"></Rectangle>
<Rectangle Margin="10" Fill="Red" Width="40" Height="40"></Rectangle>
<Rectangle Margin="10" Fill="Red" Width="40" Height="40"></Rectangle>
<Rectangle Margin="10" Fill="Red" Width="40" Height="40"></Rectangle>
</WrapPanel>
</Grid>

Answer 1

It looks like you forgot to center the WrapPanel in the Column. Like this:
<Grid x:Name="root">
<Grid.ColumnDefinitions>
<ColumnDefinition Width="263*" />
<ColumnDefinition Width="240*" />
</Grid.ColumnDefinitions>
<Rectangle Fill="LightBlue"/>
<WrapPanel HorizontalAlignment="Center">
<Rectangle Margin="10" Fill="Red" Width="40" Height="40"></Rectangle>
<Rectangle Margin="10" Fill="Red" Width="40" Height="40"></Rectangle>
<Rectangle Margin="10" Fill="Red" Width="40" Height="40"></Rectangle>
<Rectangle Margin="10" Fill="Red" Width="40" Height="40"></Rectangle>
<Rectangle Margin="10" Fill="Red" Width="40" Height="40"></Rectangle>
<Rectangle Margin="10" Fill="Red" Width="40" Height="40"></Rectangle>
</WrapPanel>
</Grid>

Answer 2

You're getting the big space at the end because it can only fit so many squares in the space you've assigned it. It can't quite fit the last square in to the first line so it wraps it. That chunk of space on the right is just the extra "dead" space.
The other thing you can do with a WrapPanel is specify how big the item is going to be. You'll see I've used the ItemHeight and ItemWidth properties, this gives me more control over how it is sized.
<Grid x:Name="LayoutRoot">
<Grid.ColumnDefinitions>
<ColumnDefinition Width="263*" />
<ColumnDefinition Width="280*" />
</Grid.ColumnDefinitions>
<Rectangle Fill="LightBlue"/>
<WrapPanel ItemHeight="60" ItemWidth="60" >
<Rectangle Margin="5" Fill="Red" Width="60" Height="60"></Rectangle>
<Rectangle Margin="5" Fill="Red" Width="60" Height="60"></Rectangle>
<Rectangle Margin="5" Fill="Red" Width="60" Height="60"></Rectangle>
<Rectangle Margin="5" Fill="Red" Width="60" Height="60"></Rectangle>
<Rectangle Margin="5" Fill="Red" Width="60" Height="60"></Rectangle>
<Rectangle Margin="5" Fill="Red" Width="60" Height="60"></Rectangle>
</WrapPanel>
</Grid>