what is that you dont' feel you might not be programming securely?
for one thing, whenever you query against db, you need to put them into ParameterCollection to prevent sql injections.
In addition, password or senstive information should be encyrtped and decrypted.
On top of all these, you should have SSL for things like credit card information and all to prevent spoofing.
Just the things come up to my mind right now.