Pain with Aircast SP Walker boot

I had ankle surgery 3 week ago. The surgeon tightened 2 peroneal tendons and also put a suture on my ATF ligament. Today, the surgeon removed my stitches, then put the Aircast SP Walker boot, and he told me he could walk with it without crutches! I was scared so I walked with it with crutches, while putting some weight on my new boot. It was painful in the car, but when I came home and lie down, it was very painful, I felt like it was the same pain intensity the night of the surgery. I took paracetamol, no change. Then, I had the idea of deflating completely the aircells of my boot, and magically, the pain went away.
Did this happen because my surgeon inflated the aircells too much?
I don’t know if this Aircast SP Walker boot is a common kind of boot.
In the instructions, it says “Higher pressure gives more support when walking, lower pressure is more comfortable when sitting or reclining”.
Is walking with this boot without crutches 3 weeks after surgery too early? Initially, he told me that I would get the boot 4 weeks after surgery, but then, he said that I’m healing well.