Hi Amorphous,
I know it might be a really disappointing time for you, but let us try and see the bright side:
"I practiced so god damn hard" - you've developed a skill that's so invaluable in life outside of high school - persistence and determination. This isn't a waste, this is something that if you spent a whole year just developing and refining your determination and even if that is all you did in that year, it should still be, by any measure, counted as a successful year. You didn't waste this time, you spent it developing a quality that's far more important than entering MacRob. Every successful person has gone through differing levels of failure!
'wasted so much money' - nope, because in order to practice for the test, you must have learned a whole variety of different things - from learning how to manage your time to how to prioritise and learn content in a more effective way. Don't think of it as a waste, think of it as a valuable learning opportunity!
'last chance getting into a selective school' - I've taught over 10 Macrob students for Maths Methods/Specialist Maths as well as having many an ex-Macrob student as friends, and I can say from a first and second hand perspective, it's really not as life-defining as you think it is. I'd suggest trying to take a look and find what it is that you want to get out of the Macrob experience - it's definitely not exclusive to Macrob whatever you think it is! (unless you want to write Macrob as your high school as part of your resume or just tell people that you graduated from Macrob later down the track, but if you're chasing prestige it's 1. Not as prestigious in University anymore, plus not many pry into your high school history too much and 2. you can find a lot more satisfaction just having a few close friends!)
Also, as you've mentioned, it's been over a year, i'm sure you've experienced a whole variety of exciting events and journeys through that year. The grass isn't necessarily greener on the other side!! ^_^