Looks like you may just need to be wrapping your measure into Sum() functions so:
Conversions to aaa = IF [Funnel step] = "aaa" THEN [Number of Visits] END
Conversions to aaa = IF [Funnel step] = "aaa" THEN Sum([Number of Visits]) END
Please can you upload your workbook so we can see where you are at so far.
nb For the future, always try to upload a packaged workbook (.twbx) file pref using Superstore Sales then we get on it a lot quicker.