pressure on my Ideal mini c was about half a bar?

the pressure on my ideal mini c was about half a bar and the towel rail in my bathroom was only two thirds warm and was cold at the top . i tried bleeding the towel rail , but this did not work . As the pressure on the boiler read about half a bar i topped it up with water via the fill loop . the towel rail is now fully warm , but the pressure is now at two bars .what have i done wrong and how can i get the pressure down to 1 bar ?