For our first few novels as a new author it’s best to stick to the guidelines, certainly to a goal of 95K words. Should you be lucky enough to get an agent to represent you they’ll insist on that.
But what happens when you type The End and it’s just 65K words? Of course it’s tempting to add a sub-plot and that may be the perfect thing to do. Or you could develop your scenes and characters; think about some of your favourite novels. Yes it was the story, but you loved the characters too.
Go write. It’s the weekend.