Relax, you get all sorts of awkward goofs in the Gym. I can sympathise though. I never liked exercising in my neighbourhood because I was surrounded by a bunch of really nosey, stuck-up white people (about 60% of whom are pensioners) who would glare disaprovingly at you from their windows and cars. I used to train on my street to improve my 1.5 mile time and there would always be the stuck-up *******s in their black landrovers and shiny Volvos looking at me as though I was an escaped zoo animal while I was trying not to have a heart attack from the physical exertion. I learned to just smile at them, it makes them look away.
Rowing machine is pretty simple. Just watch someone else do it and then copy. I do find those fancy machines to be a bit awkward myself as I'm very tall. You have to start somewhere. The only cardio machines I use are the treadmill and the rowing machine as they, in my humble opinion, are the only functional machines. The eliptical is for weak/fat people. I only use the rowing machine when I feel like it though. If you want to lose weight and look good, you NEED TO TRAIN YOUR MUSCLES AS CARDIO CAN ONLY DO SO MUCH. Believe me, if you wreck your muscles, you're body will burn cals like an engine
Why are you so afraid of looking like a dweeb? Do you have an image to protect or something? Is there someone at the gym that you have a crush on? Maybe you should just aggresively embrace your dweeb-ness and confront the fact that you're not as badass as you'd like to be. This is how I stay confident. I acknowledge and am at peace with the fact that people are always going to be better than me and may even look down on me. I don't care, I'm on my own journey. Perhaps you need to deflate your own ego, as painful as that might be. I had to do this. If it's as simple as being a little embarrased, just grow some balls and make some gains. Though I will admit that exercising in solitude is best if you want to stay focused.
It just so happens that I'm cleaning up my diet as well. Because I'm in good shape and eat healthily, I thought I could get away with eating 2 6-packs of apple pies, 4 cornish pasties and 2 packets of fig rolls every week on top of my normal diet but, needless to say, it caught up with me.
Your body is addicted to the sugar like a drug. When you stop, you'll experience whithdrawl symptoms (late night cravings, maybe some drowsiness etc) but eventually, you'll reach a point where you wonder why you felt the need to eat all of that junk in the first place. Your testosterone will increase and you'll have an easier time burning fat and building muscles. Embrace discomfort, it's good for you.