Size of skimmer vac hose opening - inground pool

We have a new skimmer installed when our pool was renovated last year. I have a robot cleaner, so haven't had to use our vac hose till now. And I find that the 1-1/2" hose connector end of my vac hose is too big to fit into the skimmer vac opening. I understand the inground pool standard is 1-1/2" so I'm puzzled as to why my standard hose won't fit. Any ideas? I have called the pool company but am hoping someone might have some suggestions before I hear back from them.