Actually the real issue with this sentence is "even a better place". You really can't phrase it that way. It has to be "an even better place".
Regarding "at" at the end: there's an oft-quoted rule that sentences shouldn't end with prepositions, but really it's one of those rules that needs to be broken quite a lot, especially in speech. What the app wants you to do here is to say "...an even better place at which to spend time". Writing it according to the rule is fine. If you were to speak that way in a regular conversation, native speakers would think you were being very formal.
It's said that Winston Churchill once ridiculed this rule, saying something like "Ending a sentence with a preposition is the kind of thing up with which I will not put" (the joke being that this sentence observes the rule, but is a very awkward way of speaking that most people would never use).