Why did you only choose two AS levels to begin with? If you drop your business at AS level, and then just continue with economics to A-level, then you will only have one A-level and one AS level, which won't be anywhere near enough to get you into uni.
Your teacher is right that most unis want three a-levels and an as-level (or at least, that's the bare minimum of what most applicants have when applying). What are you hoping to study and where?