No bashing! You did good!!
I always take it away from them at 4 weeks in the basement, which is roughly the same temps. 50-60 depending on the day. They did just fine.
I hardened the babies off by opening the windows in the basement in February. Had 5 week old chicks in there with roughly 35-40 degrees. They feathered out quicker this way, and I believe will do better in the long run.
To the Original Poster:
Please read my fire safety thread, and make sure what you do with your heat lamps outside is done properly. Please don't use extension cords.. Fire marshall told me that is an accident waiting to happen.
No Bashing here either. i do use an extension cord, but being in the electrical business, the cord is not something you will find at Wally World.