Boardwalk sections

I’m trying to figure out why I can’t make any more boardwalk section I have very few of them and I want to expand my boardwalk can somebody please help me and tell me what’s going on every time I click the thing to make it it tells me that I’ve exceeded my amount I don’t understand how I have very few my boardwalk is very little but I could still expand the water so I don’t get it to someone please help