Proud of you.
Guys who know about fitness and more big muscle guys than you realize know what it takes, and many were super fat or really small and thin to start. Ask questions. I understand you are shy, just don't worry. Look like you want to know. Guys will be glad help you right up to the most muscular, sometimes if you don't ask. Just make sure they know what they are saying, which is easier to figure out as you get more advice from lots of people on working out. You will find some guys don't care or don't talk, and others like to work with you. It helps you to get to know people, too, at least as acquaintances at the gym.
Unfortunately, some guys at the gym are definitely conceited, rude, or have on and off mood swings. Others have distorted self concepts because they are muscular, or they think they are! This is just a group of people to ignore. They are powerless because most people are usually not like this. Fit or muscle gods, if you get to know them, they may tell you about what they need to work on and see it as a work in progress just like you. It's your gym as much as theirs, and you are at the gym for the same reason. Most people understand this.
Guys at the gyms range from thinner than you to obese of all ages, in shape and out of shape. You look in shape and want to gain muscle. You are just right to go the gym and lift weight aside of any other guy not matter how muscular he is. You are doing the same thing.