This is why I buy at least one more packet of yeast than I calculate is needed - cheap insurance. In this case sounds like it could have helped reduce any anxiety. I too promised myself to never go back to the under-pitched beers I made of yester-years! Sounds like all is going well. Now that ferment is underway, good temp control will help too. Hopefully you added nutrient during the boil, which will also helps ensure a healthy ferment. I use the Wyeast beer nutrient added last 10 minutes of the boil for every batch of beer I make.
As brewinhard stated, another trick to use if in that situation, is to carefully rehydrate the yeast that you have on hand, which results in a higher percentage of yeast cells that live to grow and reproduce in your wort.