Yes, you underpitched, I believe the white labs are all designed for a starter to be made. It is still building a few billion fellow yeasties (depends on O.G.?) in order to take on the job.
1. You did not aerate sufficiently.
2. The star-san you added to it was over the correct dilution rate.
3. The temperature at pitching was too high.
4. The fermentation temperature is too low.
5. Any combination of or all of the above.
If you don't want to wait, I'd suggest pitching the notty, If you want to wait and your sanitation practices are sound (And no other problems as stated above), it should take off in a few more days (Depends on O.G.).