Fuzzy the same thing also happened to me with the clearblue weeks. If you look online it tells you the amount of HCG it has as the benchmarks to determine the weeks, but every woman varies as to how much HCG they'll have at different points - the tests are definitely a blunt instrument.
I took one at one or two days before 3 weeks and got 2-3 and then took one the next week and got 3+. I think you should only be concerned if it suddenly goes down to 1-2 weeks or says Not Pregnant.
I've seen SO MANY women online freaking out about the weeks predictor, but the fact is, it's not 100% accurate - it even says that in the instruction leaflet. So please don't get too upset about it. xxx