Some much appreciated help

Well, I played my first ever PvP match just a couple days ago, went smashingly, and it felt amazing. Unfortunately, I know what happened will likely never happen again and I'd love some pointers. I main a for top, on mid, and am working for a on bot support.

Anywhoot, in my first ever PvP I called top in picks, no one said differently or auto-locked, so I grab Tryn, and then a and some other top champ were picked, along with a mid and jng. So I was scared of no ADC, all was locked, we start and I go top, so do two others. Neither players were responsive or moved to another lane, bot was empty, so I tried building an ADC Tryn, stupid I know. I was against a and a . All seemed hopeless, as this was my first PvP, but to my amazement, I killed Zac and he fled to top. fed me a bit for some reason, we won the game and I dominated.

I know for a fact this should NOT have happened and I'd love some pointers, in general and for what to do if this happens again. I know about warding, the meta, all the basics really. Thanks to all who reply!