Hello, Welcome to Just Answer and thanks for your question. Have you used meth? How often and how recently?
If you are a one-time user, generally it isn't detectable more than 7-8 hours after the last use. However, it you use frequently it is detectable for 2-3 days, and there is no way to change that other than refraining from using the drug. I'm sorry to be the bearer of bad news.
Not with a lab test there isn't. That is the reason for a GC/MS lab test. Every chemical has its own individual "fingerprint" for want of a better word, so that there are no "false positives" with lab equipment that you can get with a dipstick-style assay/screening test. If a lab test says meth, then meth it is.
I'm so sorry, but those facts won't affect the results of the test. Do be sure to drink some water before you are tested, but not an enormous amount since that will dilute the urine and is considered tampering with the test results. They do check specific gravity and creatinine to make sure the sample is not too dilute.