At some point on your journey in Christianity, you may come face to face with the possibility that you are not as 'saved' as you thought you were. I thoroughly recommend this experience. Seriously.
Not everyone who follows Christ will find an agonising experience in working out their state of salvation, but everyone who is saved should consider this at some point (Philippians 2:12, 2Corinthians 13:5). It is how you respond to this challenge to your 'faith' which speaks the most about your spiritual condition.
Some will shrug off these feelings casually, or by the power of their will ignore them. Others will not be able to rest until they have an answer; and if it is nay, they will not rest until they have found salvation.
If you are struggling with assurance that you are Christ's and he is yours, take the time to pray to God for help. Then reflect on your walk so far, and consider what the scriptures say about those who are saved. The book of 1 John was written for this purpose, for you to know the truth of your position. Read it, and search the scriptures ceaselessly, until you have an abiding assurance.