As far as getting caught with THC in your system, it should not be a problem unless you get drug tested at work / school etc. You should not worry about your doctors testing for THC unless you (or your parents) ask them to test for THC. Even if they do find THC in your system, they are not going to tell the authorities. I tell my doctors that I smoke, because it helps them diagnose me if I am sick, and they have never told my parents or anyone else. Doctor-Patient Confidentially

. Also, THC is only detectable for about a month (varies depending on the type of test).
In terms of getting caught smoking / with weed:
As long as you do not do anything stupid, you shouldn't get caught. Unfortunately, while blazed it is easy to do something stupid. Here are what I would do:
Do not carry marijuana, or any marijuana paraphernalia around with you while you are high in public. This includes lighters that were used, papers, bowls, even eye-drops. That way, if you are stopped / questioned, they have nothing on you. The likely hood that you will be questioned even while blazed is minimal, but this will help to quell your paranoia. Even if you do do something stupid, and they question you, if you have nothing on you then the cops will have no proof.
Use eye-drops. Many people argue that Rohto are the best, but any redness relief eyedrops will work. Use hand sanitizer on your hands to eliminate the smell, or wash your hands. Gum (or any food / drink besides water) will eliminate weed breath. Wear deodorant if your clothes smell (not too much that its obvious). Store your weed and paraphernalia at home in a container that doesn't let smell out.
If you do get caught by the police, all is not lost. My friend got stopped by the police while smoking in his car. He collected all the weed and paraphernalia and put it on his lap so it would be easier for the cop. The cop took the stuff, but did not write him up. At least in Massachusetts, cops would rather just throw the weed in the woods somewhere than write you up for possession because there is a ton of paperwork and extra work that goes into weed-related citations (as long as you are carrying a small amount, in Massachusetts over an ounce is considered possession with intent to distribute, so check your state laws).
And Remember:
And protip: no one knows that you are baked.