Don’t post your license number as it compromises it and others could use it and the number could be blocked as it would be exceeding the license volume, use the modify button in your post and Remove it.
Once avast IS installed double click the license.avastlic file that you should have received that should insert it for you.
If you haven’t a copy of the license file - use the Resend avast License http://www.avast.com/resend-license-paid.php function, you will need to enter the email that you used when purchasing the license, e.g. the one that the original email with the link was sent.