If you already have a doctor's appointment, I wouldn't waste the money on another test. They can do urine and blood tests, and by that time, they'd be pretty accurate. It's two weeks away, and it's going to be hard to wait because I'm sure you want to know, and you can take another test, but they're more than likely going to do a test for you at your visit so I'd wait.
I would wait a week then retest with first morning urine. It may be too early to detect the HCG or there may just be another reason you are late, which you should discuss with your doctor when you go on the 22nd. Good luck and I hope it is good news for you.