I doubt it. Most young men do have traces of semen in their urine and that is normal. But if you're worried about it, just don't jack off before your MEPS processing date. You'll need to get used to very limited time available to jack off once you are in the military and until you get used to the rules, schedules, and routines enough to be able to find any time alone to jack off once you get to boot camp and live in barracks with loads of other men and are never alone, even to take a crap or any other male bodily functions with zero privacy. You'll get used to it real quick and all of the other men will face the same thing together as a group. Don't worry all men masturbate, especially with no access to any females for sex and young men all being way too horny to stand going without ejaculations to relieve the pent up sperm pressures and urges all men have. All men do it and need it a lot. Buddies sometimes will work out how to do it and not get caught.