A higher amp esc usually has lower internal resistance therefore a higher voltage delivery to the motor. About you 45amp esc with your 2000kv motor on a 3s pack it should work but I would recomend not changing to a motor with a higher kv on 3s. And please don't put on a prop with a bigger diameter and water cool everything especially the esc. You ask should you have order a higher amp esc and I would say absolutely. You should have gone for something higher like 90amps or above.