So was I ! For some reason, most schools teach modern languages as they teach latin : you learn grammar rules, you memorize long lists of uncommon words and then use it to study centuries-old litterature. Oh, and you do all this surrounded by people whith different levels in the language. This way of learning/teaching might be great for your culture, but you should not be surprised if all you can say when you get to Mexico is si or no. Having a bad record of language learning at school means absolutely nothing on your abilities to learn a living language on your own.