Help gain weight? I’m 16 yo male, 5’5”, 108 pounds. 4% Body Fat

Hi, as the title says, I’m a short and skinny male. I calculated my body fat in two different websites and they told me 3.7% (calculator.net) and 4% (active.com). That seems pretty low, but they might not be entirely accurate. I am pretty slim but I don’t think 4% body fat thin, you know? Anyhow, I’d like to gain weight, preferably muscle although I don’t think some fat will harm me. I eat pretty healthy; olive oil, vegetables, protein, avoid sauces and butter, etc. Any help/advice you could give me will be greatly appreciated 🙂