You now know the basics of everything you need to know to create pages which people will pay for. You probably need more practise to get the pages right but the principles should be there.
What you need to do now is to keep making sites. You can always look up extra help if you need to do the odd thing you do not know how to do.
- for PHP you should always start with php.net
- for SQL start with the MySQL documentation but also look elsewhere (if you do a general Web search for PHP SQL thingyouarelookingfor it should work)
- for anything you can try a Web search for (e.g.) PHP arrays or SQL insert and you will probably end up on the above sites anyway
Do enough of that and you may never need this site again. However, there is much more for those who prefer to be guided through their development. Do some more practising first though.