To be honest, I am not very knowledgeable if it comes to botanical things. However, "ipomoea grandiflora" seems to be an outdated term which has been (wrongly) applied to a multitude of Convolvulaceae. Check out this discussion:
https://davesgarden.com/...unity/forums/t/986703/#bSo no way to tell whether or not you are looking at the right plant, sorry.