I think I screwed up using my small iPhone instead of using my computer.
My feedback to Isaac is that after creating the new custom island with the faulty pasting it made the Whole portal show same error message not only the created island
That is correct. And there is a warning on the Custom Portal Island editor about that exactly.
The warning reads:
Warning: Invalid PHP code that has syntax errors can result in breaking the entire portal.
The control panel does not use any code from custom islands, so you should be able to visit the control panel and correct your php syntax errors.