Do you believe your salvation and admittance into Paradise is guaranteed?

To be more clear I am directing this towards Christians. Now before you start to think, "Well I have accepted Christ as my Lord and savior...so of course yes I'm 100% sure I'll go to Paradise." I want you to ask yourself what is required to truely believe and be accepted as a believer? I ask this because when I bring up the question, "Would Hitler who was a Christian go to Heaven since all his sins will be forgiven by Jesus since Hitler accepted Jesus' sacrafice?" Well any Christian will say, "No, the horrible things he did proves he didn't really believe". Well then where is the line between belief and disbelief? Although in that case it seems clear and that you can easily distinguise yourself from Hitler, but what IF say you are a generally good person but you like to gossip a lot? Backbiting and slandering are serious sins and what if God/Jesus see this as a sign/act of disblief and say you are going to Hell? What if you are a good person but you gamble a lot and God doesn't take it too lightly? I know you're thinking you're forgiven of these simple day to day sins, but what if in God's eyes you are an unbeliever because you sin each and every day? Are you so sure your efforts are good enough? If you don't think your works matter, is your faith good enough? You say it is so, but only God knows the weight of the faith in your heart. What if on the Day of Judgement you're all happy to see Jesus and get into heaven, when God tells you your belief was not strong enough and that you held more disbelief than belief? Just remember only God will judge us, and it is not you or anyone else who KNOWS you will go to Heaven, but doing all you can to make sure it is likely is something we should all think about.