I'm Confused about the MEPS UA Process?

You will be done for the meantime. Once you arrive at bootcamp they will test you again in the first couple of days. There is no testing at a lower level, from the test the military does they can tell if you were just "around" it or smoked and with the military a fail is a fail no matter how minute. Also if your recruiter gives two cents about getting you in he should give you a drug test at the office before hand just to make sure in case he needs to delay your entry.