I made the same mistake with the weapon upgrades on my first run. There's that other trophy that causes you to do it!
Going back from the end of the game is a good idea. I'll do that. One question: how many tonics do you get from rescuing little sisters? i know after the first three you get one, but i didnt get any after that, however i didnt rescue every little sister in the game (i did that trophy on my survivor run and the early big daddies are not fun to fight) so i didnt get given all the possible rewards.