Advice needed... Newbie here please reply

Ladies Saturday 20th Aug we found out we were pregnant. Bought a clear blue week indicator that said 2-3 which means I would have been between 4-5 weeks pregnant. I then Googled how to work out your potential due date by entering the first day of your last period which was 4th July. Downloaded this app that says I am 6 weeks 3 days ( I think) just out of interest I had another clear blue weeks indicator test so thought I would take it expecting the result to read pregnant 3+, because according to the app I'm about 6 weeks pregnant. it didn't it still sayed pregnant 2-3. Really worried, am I worrying for nothing or have I worked it out wrong?