Hi Nater! Welcome to the Vaping Underground forums! You're getting a lot of REALLY solid advice. Hate to say, but those guys in the vape shops are sometimes pretty new themselves, and have NO business giving out advice, let alone handing .3ohm mechs to total beginners... Nobody would be telling you this stuff, if they didn't care.
Do you mind telling us what BATTERY them guys sold you, for that build? There are only about a half dozen battery models in existence, that should be used in a setup like that, and I'm thinking I have about a 50/50 chance that the one they sold you, isn't ONE of em..
Don't take advice personal, everybody has good reason to make sure you learn what's up, before you hurt yourself. Those news stories with people missing teeth are REALLY bad for our image, AND those peoples teeth..
Enjoy yourself here! You lucked out, found a GREAT place to learn!