Well, if it was easy it wouldn't be near as much fun when you catch one, right?
If you feel pretty confident you were not spooking them too much with your approach, think about a couple other variables. Anywhere there's a rock, tree or bend in the stream is a likely spot. They all scour out a little deeper water and offer more protection. They also concentrate flows and the food floating by. Seams where fast and slow water are adjacent to each other are good too. Along the edge of a rock, below a plunge in the slower-current "V", to the sides of a plunge in the eddies, along the foam line at the start of a run. Hit all those places.
In such skinny water, your mistakes are magnified. In a bathtub-sized pool, if you slap a fly on the surface, lay down a big coil of tippet, plop a fly in with a split shot and indicator, stick a fly in a tree and shake the branch overhead, whatever, you will make those fish quit or leave. And if they dart out of there, they're gonna spook their buddies too.
I believe presentation trumps fly selection most of the time. And, that's really the hardest part to learn in fly fishing. You've surely read about drag-free drifts, etc. Laying a dry fly on the surface and having it float along in the conflicting currents without creating a wake is a bit of an art. Having a nymph bump along at the right speed below the surface, where you can't see it and the current is probably different than at the surface, is an art too.
Anyhoo -- keep at it.