Hello
@Rory congrats on your first 2 games. Regarding the control element, don't worry about it. Every ref has gotten to points where they have practically lost control, especially in the early days. More than likely you didn't lose control, but you just didn't give the impression you were fully confident in yourself.
Body language, body language, body language. It is everything. You can make an incorrect decision, but if you make it with total confidence and can sell it with a handful of words, you can get away with a lot of errors. Obviously the idea is to not make them in the first place, but for when you inevitably do, your confident body language and tone will get you out of the hole. When people feel you are confident in what you are doing, they'll tend to back off. When they sense you are unsure (and believe me they will as you saw) they will pounce on it and try to destroy your confidence and confuse you. In essence they want to psychologically manipulate you so they can control the game through you, to the benefit of their team.
In this situation you had, it should have been a straight red as others have said (offinabus). If it was a case he said it quietly and nobody heard, you may have even been able to let it slide (enough trouble will find you, you don't have to go looking for it with a "I heard that!"). The idea of trying to get him subbed is a good idea but I would suggest you reserve that for less severe cases, i.e. not straight reds (serious foul play, offinabus, violent conduct etc). You may wish to do what you did when you have a player on a yellow and he doesn't appear to be calming down with his challenges. You go over and say "I suggest you change #5, he is on a yellow and is playing like he wants another". You are alerting the coach to a problem, and you are giving him a solution. Human behaviour is to take the solution when posed a problem.
The solution element is key, "ref our keeper hasn't got a keeper jersey, he wants to wear a nike black jersey" .. "ok no problem, wear the black but just stick a bib on top so you don't clash with my kit, thanks". Rather than "you must find a keeper jersey otherwise you can't play". You provide solutions that suit your needs and also provide them a pathway to fulfill their needs (which in reality are your own wants and wishes). Yes it's manipulative, but it's for the greater good
You could write a book about referee interactions, you will eventually pick it all up. For now, body language, and brush yourself up on the laws. This will give confidence which will help you mentally on the pitch. Lastly, one of the easiest ways to lose control of a game is bad foul identification. Missed fouls = feelings of injustice = wanting revenge = war. Perhaps find some sources to sharpen your foul identification skills to make sure this doesn't happen.