Beyond the missed stop, you really need to evaluate your weights. You should have very little to no air in your BC at the end of the dive. The fact that you need to vent a good bit of air indicates to me that you are over weighted. Being over weighted requires a large air volume in your BC to compensate for the excessive weight. That large volume of air makes it more difficult to control buoyancy, esp for a new diver, which in turn makes it much more likely for a run away accent to occur. Many divers do not properly vent their BC's and incorrectly think more weight is needed when in fact, proper venting to remove excessive air in the BC is the real problem. As a first step, I would recommend doing a good weight check and maybe a buoyancy class with a good instructor.
