you can't know that you are going to heaven. you might hope, but until you cash in, it's only a hope. nobody has come back with a tally of what percentage of self-assured christians actually got in. maybe it's 100%, but that seems unlikely.
it's much easier to know that you aren't going. in my case, i'm a well-known scumbag so i know exactly where i'm going. the problem is, there's not a thing i can do about it. all the well-meaning christians will wring their hands and tell me how god loves me blah, blah, blah, but at the end of the day, that just doesn't cut it. knowing that, i'm automatically exluded from heaven.
so here's the bottom line: you CAN be assured that you're right when you think you're going off to eternal torture, but it's not at all clear whether any person is good enough to be ASSURED they are going to heaven. but, if you can convince yourself of that, it must be very comforting.
Now, to answer the question about whether i consider myself to be a good person.... that should be obvious from the above