Since you said you believe there is a heaven and that you have behaved well enough to go there, you apparently believe there is a God who offers heaven as a reward for those who in some way deserve it.

There is a very basic problem with saying there are no moral absolutes and that everyone decides for themselves what is right and wrong.  This is one of those clear cut answers God gave us in the Bible.  God is very clear that there are absolutes, and that we should obey them; and if we don't we will be judged!  The 10 commandments are a prime example, in fact the reason we have them engraved over our US supreme court building is that the founding fathers recognized that even our government needed the moral foundation that God provided through the 10 commandments.  We as individuals need it even more, our eternities are at stake.

If there is a God who is the final judge of our actions, He must also set the standard for those actions.  Otherwise there could be no real justice.  Everyone would just do what is right in their own eyes.  Hitler thought he was doing the right thing, and had no remorse for his actions.  Osama Bin Laden feels he deserves a reward for his terrorism, which he believes honors God.  Everyone can't be right.  God has to set the standard. 

That's why we are so thankful that He left us His Word, so we will know what He expects. 

Click here to take a little test based on the Bible that tells us if we've been "good enough".