Avery numbers identify both the label size and arrangment on the page as well as the type of label (transparent, ink jet, etc. ...)
Check for an Avery number with identical dimensions. This info is often on the label package somewhere. If you can find an equivalent, you can specify that Avery number instead of 5168 and the layout wizard will create your layout for you.
To set up a layout from just the label dimensions can be done but requires paying close attention to key details and sometimes you need to adjust the resulting part sizes by amounts of as little as a single pixel before it all prints correctly.
The height of the label should measure the distance from the top of one row of labels to the top of the next row. This will take into account any space that may exist between the labels. Then the header layout part needs to be exactly the same height as the distance from the top edge of the label page to the top edge of the first label row.
You can make very small precise adjustments to layout parts by clicking a part label to select it and then editing the height showin in the height box in the inspector's position tab. (Click the units shown next to these boxes until you get pixels first.)