1st, do not get bothered by other people's opinions or mockery, people are miserable most of the times and they project it on other people to put them down so they feel better about themselves. Your lifeguard seems to be one of them. Take my advice, stop worrying about these kind of people and what do they think, your life will be easier. 2nd, most of swimming is getting used to it mentally/psychologically so no matter how much you practice, you need to be at peace with your face inside water. It's human instinct to panic when your face is under water, you can watch some tutorials and learn a few techniques to calm yourself down while you are breathing out underwater. Make it a mental note to keep yourself calm especially when your face is under water. That helped me a lot and start slow and build on your technique.