I gave my bank account log in and username along with security answers to someone. If I changed my username and password as well as my security questions, could I still be scammed later on?
It’s down to bank processes regarding such changes. Besides, the potential scammer may have your name, address, bank account numbers etc, not just your login details. They can bypass internet banking and try their luck at a physical branch.
If you’re concerned about this, ask the bank to close your bank (money) accounts and your internet-banking (login) account, and start again. Open new accounts and re-register for internet banking. Unless you have a lot of direct debits or direct credits, this shouldn’t be too much of a hassle for the sake of your peace of mind.
As @ceejayoz comments below, you can also do the ‘starting again’ part at a different bank to avoid any holdover whatsoever from the old accounts.