Yes, I suspect that you should use 3.3V.
You should never trust Ebay sellers. Sometimes they lie. Sometimes they are just ignorant. Sometimes they know what they are talking about.
Please read the part number of Q1 on the pcb.
The 2.4 inch displays take much more power than 0.96 or 1.3 or 1.54 inch OLEDs.
But nothing should be "hot".
David.