[renegade]

Don't beat yourself up, it's just the luck of the draw. There's no way you could have known his travel pattern. You said you just found a scrape and set up on it. So you guessed which tree would give you the best shot at the scrape should he visit it. Had he done as predicted you'd have been in luck, but buck are not predictable during the rut, especially since you had no prior knowledge of this buck or his habits. Chalk it up to the learning curve.
But the issue you could have avoided (at least 8 out of 10 times) was as theotis mentioned. As soon as you hear anything that could possibly be linked to a deer.... get ready! I tend to stand a lot so that I can rotate in the direction needed as soon as possible. And any movements, deer present or not, must be fluid and slow, so as not to draw any attention from even a bird. So you need that additional time so you don't have to rush things. Twenty feet up is usually good unless the understory is sparse and your easily silhouetted. Maybe you needed more height.
Remember, archery is a close contact sport. Your senses against his. That won't be the last time you get busted. Good luck.