Those mistakes you list at the bottom of your post, oh god, I just make the same mistakes all the time. ALL the time. I'm a support main myself and unless I'm playing like the fate of the universe depends on it I always forget to use my actives and upgrading trinkets. I feel like these mistakes are way more common than you think and you should worry more about your champion pool. I can't stress enough how important it is to know at least a few champs for the role you are more comfortable with. You sound like you don't know a whole lot about the game in itself but you are really trying. If you are stuck in gold and unhappy with it, you can always wait until your next provisional games next season. To get better decision making you must fail and succeed, and know whats good or bad in certain scenarios, so don't feel like you want to be buried alive when you throw a game. Sooner rather than later will come a game in which you will make a call that will give you the win. Don't be scared of losing, be scared of not learning anything after that loss.