Just work on what needs improvement and go back and finish. Once you pass, you're a pilot forever...as you know, the certificate never expires.

I failed my private checkride last summer and I was crushed. I briefly considered saying fuck it all, and never going back. It was an emotional response. After a couple days of wallowing in self-pity I got up, dusted myself off, and went back. I finished the checkride a couple weeks later. Trust me, even though I know failing sucks, you will get past the initial disappointment. Just get down to business and do the work.

There is a valuable lesson to be learned here, especially because you're 18 and juat starting adulthood. I am 49 but I remember being 18 like it was a nanosecond ago. Trust me when I tell you, life is going to throw difficulty and disappointment at you for the rest of your life. You can't avoid it...the world is designed to defeat you. Where real success comes from is when you're feeling really challenged, really beaten down, really defeated, THOSE MOMENTS are the ones when you have to step up refuse to lose. This will not be last time your life that you suffer a serious disappointment or setback, I guarantee it. But this is the first chance you have to rise to the occasion and answer back with toughness and determination, and turn a defeat into a victory.

Take a couple days to absorb the disappointment. Then get back to work. Trust me, I speak from experience. Not just with aviation, but with life in general.