The reason I was told that it would invalidate a confession because it using it as an excuse to sin.
I just want to ask one last question one this topic. This will be the last time I ask a confession validity or mortal sin question. I’m really sorry for this. So today at confession while I was receiving my penance I had the feeling that I forgot to mention a sin. Since I was embarrassed to stop him and I didn’t remember the sin I forgot, I let him continue and did not attempt to remember any sin I may have forgotten (I had already interrupted him once while he was assigning the penance because I hadn’t finished confessing the sins I remembered). While saying the act of contrition a sin that I had thought about confessing popped into my mind. I quickly dismissed this as scrupulosity. Although, I wasn’t quite sure that my assessment was correct. I think I wanted to dismiss it so that I wouldn’t have to interrupt the priest; I was already embarrassed because of my first interruption. The action in question involved me doing something I thought would be mortally sinful, prior to the action, but the reason I thought this was purely do to OCD. So did my lack of mentioning this invalidate my confession?
PS. I have taken your advice to find a confessor, but it takes time and I’m not always able to ask a priest these questions. So this becomes the best place to ask.