You have learned a very valuable lesson about not giving a number first. Let the other side give a number first, and if you absolutely have to give a number, gi

You have learned a very valuable lesson about not giving a number first. Let the other side give a number first, and if you absolutely have to give a number, give a wide range (e.g. $30-$100). That said, you cannot change the past. What you can do now is say that as you have explored other available opportunities and after getting deeper into the responsibilities of the role (e.g. there is a management component not previously discussed) you believe that $50-$80 is a more appropriate range. Of course it is possible that the ad you saw was targeted at US based candidates and there is a different salary range for candidates in your region.