To think you can loose salvation it simply means you don’t know how you got to Christ….and that might mean you don’t even believe in Christ.
If you think you came to Christ on your own then you have a reason to believe you can lose salvation because the way you came that’s the way you will go back.
A true believe never brought him/her self to Christ but God did.
So if God brought you to Christ then Christ promised not to loose any of those the Father brought to him.
Everyone the Father gives me will come to me, and whoever comes to me I will certainly not turn away. For I have come down from heaven to do not my own will but the will of the One who sent me. And this is the will of the One who sent me: that I should not lose any of all those he has given me but should raise them up on the Last Day.
Yochanan (Jhn) 6:37-39 CJB
Extra Scriptures of assurance: