Game thinks entrance hasn't been built and won't allow me to Test/Open

[RankLord123]

New to this game, and I built my custom roller coaster (the mini roller coaster). However, I've been trying for an hour to test or open but I can't because the game says "entrance not yet built despite me having placed one in every possible position and orientation. Screenshot attached.

Am I doing something wrong? Help much appreciated.

[Gymnasiast]

Please upload your save.