It is not too late to amend your filing. If the case had already been decided in court, it would be too late.
But you are not suing twice for the same thing, in this case. You are just suing once but amending your complaint before the judge hears the case and issues the ruling.
The clerk at the court will be able to help you complete the proper paperwork to amend.
When you go to court ask the judge if you amend your claim as new information has come to light. The judge will take this into account. A judge always has final say.