Tried "Burping" my Supra's cooling system
 

So for the past few months my Low Coolant light has been flashing on and off while I drive, so I did some research and someone believed that it was air pockets in my cooling system and that I should burp it. So I just tried to do this myself by removing the radiator cap and starting the engine. After about a minute of the engine running, the coolant from my radiator just started to overflow from the top instead of bubbles burping out. So I immediately just turned of the car. I'm not sure if I did the burping process incorrectly or not, or hopefully I didn't just dig myself into a deeper hole. Does anyone have any suggestions or advice on what I might have done wrong?

Thanks