What is the name of this 70's or 80's movie about a plain girl who falls overboard while they are making movie or is left behind and follows the actors and gets lost in sea and wakes up in a island where all the things from the movie are truly happening? I think it has pirates in it. I saw it when I was a little kid and I don't remember much.

Could you be thinking of The Pirate Movie? The Pirate Movie (1982) - IMDb

The Pirate Movie was a musical and a remake of The Pirates of Penzance. Don't think that is the correct movie

It does sound exactly like "The Pirate Movie".

From Wikipedia:
Mabel Stanley is an introverted girl yearning for popularity in a seaside community in Australia. She attends a local pirate festival featuring a swordplay demonstration led by a curly-haired instructor, Frederic, who then invites her for a ride on his boat. She is duped by her acquaintances into missing the launch, so she rents a small sailboat to give chase. A sudden storm throws her overboard, and she washes up on a beach. She subsequently dreams an adventure that takes place a century before. In this fantasy sequence, the swordplay instructor is now named Frederic, a young apprentice of the Pirates of Penzance, celebrating his 21st birthday on a pirate vessel. Frederic refuses an invitation from the Pirate King, his adoptive father, to become a full pirate, as his birth parents were murdered by their contemporaries. Frederic swears to avenge their deaths and is forced off the ship on a small boat.

The Pirate Movie - Wikipedia, the free encyclopedia

Here's the movie~if you're curious:
The Pirate Movie - YouTube
Did you check it out to see if it would stir memories?

I can think of other stories-come-to-life, such as "Magic Island", but they don't match your description at all. They generally star males, not females, in the lead.