I asked for Salvation, but wasn't sure if I was 100% sincere.

A few months ago, I watched this video on the after life. On this video, a certain, proclaimed minister witnessed an experience God had given him in which god showed him Hell. Now, this video got me to thinking about my situation, and where I stood with God. Quite honestly, this video scared me to death, because it portrayed such a vivid picture of Hell, and told things of it that I never would have imagined. More or less, this video scared me straight, and made me want to do something about it. I'm not sure if right then I re claimed my life with the Lord, or if it was later, but I certainly did ask Jesus into my heart. Now, here is the tricky part, I wasn't sure if I was sincere or not. I know that sounds like a travesty, but it's hard to explain. I don't want to call a lack of belief, but sometimes I feel like that's what it is. I know there is all the proof in the world that God and Jesus Christ exist, and all the events in the Bible were real, but why can't I just make myself quit doubting? Never the less, I asked Jesus into my heart, so right then, the Holy Spirit should have netered my life, right? I struggle everyday in my Christian walk. I am constantly burdened with spiritual confusion and doubts. I am forever questioning my salvation. The only proof of the Holy Spirit I have in my life is that I am reminded of right and wrong, and occasionally the spirit will point something out to me in the Bible that I need to know and apply. I am feeling really discouraged ladies and gentlemen. I feel like I did something wrong. I have always been told that it is not uncommon for a Christian to have doubts, but in my case, I really think Satan is out to get me. I try my best everyday to live a life that is pleasing to God, but I fail. I know that salvation is not earned, but is a free gift in which, hopefully, I recieved. i know the Holy Spirit is supposed to help me change and live a life more pleasing to God, but what is my part? Do I need to put forth effort in this change, or do I just let go and give it all to the spirit??? This is torment, and quite frankly, it's eating me up. Someone please help me. One more thing, am I wrong for coming to God because of the fear of Hell. I surely don't want that to be my only reason I serve him, but selfish me, that's all I have. I wish my love extended further than that for God, that just sounds so selfish.