"The store is there."
It should be. From the English you can't tell if it's near the listener or elsewhere.
Also mukou was translated as "over there" in this same lesson, how is it different?
I don't quite understand the difference between achira and sochira in this instance
Yeah, in english "there" could mean both and you wouldn't know which to use, both are correct. They could use "over there" to mean あちら though. Just remember こ is near the speaker, そ is near the listener and あ is far from both. This way you can understand the sentence in japanese without having to translate it.