Yes, to back up what hivrhh has said to you, a three month test is considered accurate - any test before this time is highly indicative but not definitive.
When someone becomes infected with hiv, they go through what is known as seroconversion, which means they go from negative to positive hiv status. This usually occurs within six weeks, but very rarely up to three months. After seroconversion, hiv antibodies, produced by the immune system, are detectable by a standard elisa antibody test. This means that for most people, a six week test does indeed give an accurate result, but to be safe, the 13 week test is wise, just to be sure.
And it's true, terry really does not know what he is talking about.