Received Duplicate Invisalign Trays?

I started Invisalign on July 1st and received trays 1-3. Tray 3 was made of a more flexible material and didn't have the same tightness as 1 & 2. I went to the dentist today to get new trays and they said I am continuing with tray 3. They gave me a new tray 3 that is the same thick plastic as trays 1 & 2. Did they mess up and give me something I shouldn't have worn for two weeks? The new tray 3 is extremely tight and I am feeling more pressure than I did with tray 2.