First, stop lying. Come clean and apologize for the lie, explaining why you weren't comfortable being honest. Second, remember you can be a well behaved smart kid with piercings, so don't play into the expectations of being a bad kid just because you're someone who may get a tattoo or three later in life. If you want to have a serious discussion about it with your mom, first look at what you can do to meet her expectations. Are you well behaved, punctual, kind, and studious? If not, think about getting your grades up and stop missing your curfew before starting the conversation. The more you act like an adult without being asked, the more likely they'll be able to see you as someone mature enough to make these type of decisions.
Second, come prepared both with research, and prepared to hear and accept no. Bring it up as a hypothetical, and ask if they would let you know their objections to it. Listen and be receptive to what they say. Be able to answer their questions honestly. If you can't answer what you'd do if you change your mind in 3 years or how to treat a torn or blown out lobe piercing, then you need to spend more time researching and thinking on this before you bring it up. If you don't actually listen, they won't listen to you either. If the discussion becomes heated, if they flat out say no, or if the mood gets unpleasant, stop. Ask for permission to bring it up at a later date, then drop it entirely until then (increasing your perceived maturity with more good deeds in the meantime.) Remember you're trying to be seen as mature, you need to be cool headed and respectful, especially if they are the type to get frustrated and yell "Because I said so!"
A dedicated show of maturity in general life and in your conversations with your parents won't guarantee they'll say yes, of course. But it will make a lot of thing in your life easier. It will be easier to talk to them like people, it will be easier for them to see you as a young adult instead of their little baby - meaning easier for them to say yes to other things that you may want to do. And even if they never agree, it will make them less worried when you turn 18 and start doing whatever you feel like with your body, because you'll have spent a few years showing them you make smart decisions.