Stacked Area Chart Taper on/off issue

I searched the forum and found this:
http://www.excelforum.com/excel-gene...g-to-zero.html

Which is about the same problem as i'm having, but my situation is a bit different...

Here is a sample of my data. As you can see, the graph tapers on and tapers off at the start and end of the data. I want it to go straight up and down. i've googled it and searched on forums, but can't find the solution without completely changing the structure of my data...