Stop for a moment and think about what you are trying to do.
What you want to do is take a node, print it's left graph (if any), then it's right graph (if any), then the node itself:
So if you have a binary tree:
1
/ \
2 3
/ / \
4 5 6
You want to print
4 2 5 6 3 1
Yes?
You aren't far off, but your code returns too early. Try something a little simpler:
(This is your homework, so I won't give you actual code here)
node.Print
{
if (n.Left != null) n.Left.Print()
if (n.Right != null) n.Right.Print()
Display(n.Text)
}