You might have been better off leaving it outside until the real cold weather arrived - moving it to the greenhouse means the temperature around the plant was even higher, so it thinks its spring. Crrently its not been cold enough to worry about non hardy plants. Chilly, yes, cold, no - the impatiens are still flowering in a garden next door to me here in West London.
Not much you can do about it now I'm afraid, you can't stop the flowering process if its started. If the flowers come to fruition, enjoy them while they're present is the best advice I can give, even if that's in 3 weeks...

Tree peonies are tough as old boots and shouldn't need to be taken into a greenhouse to overwinter. Worst that can happen is the top growth will get killed off and it will grow from the base again.

Well I've had mine for the three years I've been here, in a pot, and just left it outside over the winter. It hasn't died, but neither has it grown much. I've planted in the garden now and hope for bigger and better next year.

It will appreciate being in the ground Ginellie

Good news Moongrower, thank you.

Thumb up!

Many thanks guys, I shall enjoy the blooms if I get any, but at least I can relax knowing my precious peony tree will survive!
Your reassurance is much appreceiated.