So we have our tile lets go to the event sheet disable the Horizontal Grouping and place out events under the Diagonal Grouping. The first event is the 'On Start of Layout' and set the Tile bullet Angle of Motion to 45. Since you already have the X and Y events from the other two Sections all you have to do is copy them to the Vertical Grouping together your Sheet should look like this once your done.
Run your project and your background should flow seamlessly since the tile was built to conform both to the width and height of the project.
There are many ways to achieve things in Construct it all about what is suitable for you.
So I hope that this tutorial was informative and that it was able to help you. Congratulations you made it all the way through the tutorial. I know I had you bouncing between two software but with development you tend to do that alot anyway. :)
So till next time Happy Constructing.