The basic form of the argument is:
1.) Since it is possible for such things not to exist, there must be some time at which these things did not in fact exist.
2.)There must have been a time when nothing existed.
3.) If this is so, there would exist nothing that could bring anything into existence.
4.) Contingent beings, therefore, are insufficient to account for the existence of contingent beings:
5.) There must exist a necessary being whose non-existence is an impossibility, and from which the existence of all contingent beings is derived.
This is the version that your using? Or are you using another variant of the cosmological argument?