How reliable is the PCR test?

All covid case numbers we hear reported every day are based on the PCR test (Polymerase Chain Reaction). Just how reliable is it? Sars-Cov2, like many other viruses, contains genetic material called RNA which are so small they are difficult to detect. PCR tests doubles the fragments called 'cycle thresholds (C.T) and keeps doubling them until they have enough genetic material to identify. Most labs go up to 38 to 40 cycles which is an amplifications of 1 trillion times. Is that too much amplification? Genuinely sick people get a positive test after 6 cycles (64 amplifications) because they have a high viral load.