You have sliced out the correct portion of your table, however you did not realize that you can apply the string to number conversion on the entire array. Once you've got that, you can index out each column of data and assemble the plots. Also, I noticed that you selected a waveform graph instead of an X-Y. Since your X data may not be evenly spaced, and you want it defined by the table, you should use the X-Y. I have attached my modification of your VI to demonstrate.
Enjoy,
Daniel L. Press
NI Certified LabVIEW Developer
PrimeTest Corporation
www.primetest.com