Oh sweetie, you must be very worried. Sometimes hormone levels fluctuate during the day, so it might be that you happened to test the second time when they were lower, or when you'd drunk more, the conception indicator has an 8% inaccuracy rate, and that's with the first urine of the day, so nearly 1 in 10 women are going to get an inaccurate or worrying result.
I took a first response pregnancy test at 8 weeks which came up negative, I had an emergency scan but everything was fine, so the tests aren't infallible.
If you are very worried and can't wait until Friday, perhaps you could phone your doctor tomorrow and get a telephone appointment. If you estimate from your LMP that you should be 6 weeks or over, the doctor could refer you over the phone to you local EPU for a scan or blood tests, to see what is happening. If you are under 6 weeks, the doctor might be able to arrange for you to go in and have a blood test to check your Hcg levels.
But remember! That conception indicator is wrong for nearly one in ten women, you may just well be unfortunate and have had all that worry for nothing.
I'll be thinking of you, hope everything is okay.
EDIT: I've just found this on the clearblue website:
The overall accuracy of the Clearblue Conception Indicator has been clinically proven to be 92%. The accuracy of the Clearblue Conception Indicator is 96.5% in the 1-2 week range, 76.1% in the 2-3 week range and 96.9% in the 3+ weeks range.
So if it was 2-3 weeks to start with, it's only 76.1% accurate. That's not very accurate at all.