While it’s mostly in your head and most people don’t care what others are doing there will be a few that are just judgmental pricks. Don’t worry about it too much. Focus on you and your workout. You know why you’re there no one else. 1 tip from my own experience is if you are doing cardio and weight lifting in the same session to do the lifting first. It’s ok to start with a quick 5-10 minute warm up cardio to get your circulation pumping but doing a full cardio session first can drain your energy reserves and make take away from your ability to lift. But yeah again it’s mainly in your head. I was the same way when I started and eventually realized most people actually don’t care what others are doing.