Are you sure you are stuck?
I think the undersea facility winds around in a big circle. I could be wrong, but I think you can make your way around and come back from the other side.
If you are absolutely stuck, contact Pixel Support. From your game screen, choose the Settings cog (upper left or right corner). Make a note of your Player ID. Then choose the Support button. Choose a category from the bottom half of the screen.
Don't enter something in the text box at the top of the screen. That just sends your entry right back here to the player forum.