I assume that you’re speaking past tense, that you’ve already foregone the the opportunity to take AP Spanish. From an admission point of view, I agreen with gabby, it would have been better to take AP Spanish to complete 4 years of one language.
If this is still a future events, and you still have the opportunity to take a fourth year, even if it is an AP-level course that you don’t prefer.
By itself, the failure to take four years of a language will probably not be fatal to an application, but things add up. And something will be the straw that’s too much for the camel. Harvard wants you to enter college with a passable grasp, written and spoken, of a foreign language. Don’t disregard their strong preferences lightly.