You will arrive at AMS in the Schengen side of the airport, which contains Lounge 26.
Normally, but not always, the lounge will check your boarding pass for your next destination and only let you in if you're in the "correct" side of passport control.
Since you are flying to the US, you should therefore go through passport control once you arrive and head for Lounge 41 on the mezzanine level on the non-Schengen side. It's only a short walk from passport control, 2-3 minutes maximum).
I never really got the idea of why there is occasional reference to terminal numbers in Amsterdam; it's all one big terminal, but with Schengen and non-Schengen sides separated by passport control.