Yes, you made a mistake, unfortunately. It could have ended in a lot of drivers becoming frustrated and blaring their horns at you for being in their way, although it sounds like you got away with it this time because of a pedestrian phase at the lights as well as a "micro-safezone" you found while letting the pedestrians cross.
The problem you had stemmed from entering the junction when your exit wasn't clear. The colour of the lights is immaterial, as is the layout of the junction. The golden rule of any situation, junction or otherwise, is not to enter unless you can clear the situation safely.
Next time you're at that junction, look beyond the two cars in front of you. Look right and ask yourself if those two cars (and your full car length) can clear the junction completely. If the answer is a clear no, or you're just not sure, wait near the stop lines until more movement has taken place and you can reassess that answer.
If you are in the middle of the junction and your light changes from green to red, you MUST clear the junction immediately (and have the necessary room to do this). As you hinted at in your post, it is unacceptable to block oncoming traffic or traffic from your right from entering the junction.