A few things:
- An apostille is generally not required for such a petition.
- Traveling to the US as a tourist while having a pending immigration petition is not necessarily a good idea, I would check with a good lawyer first.
- I can give you a reference to a top-notch US immigration attorney. PM me for details.
I know someone in this situation. The lawyer said it is OK to travel with a pending application. There is a slight risk of encountering a hostile official but not likely. The person who posted the question needs to see a qualified immigration lawyer to do things properly.