I am not married and became pregnant while in needah status, though not with a Jewish male - with a non-Jew. I have heard that it is proper to immerse in mikveh in the 9th month. Is this true? Will this atone for any toomah? What is proper to atone for toomah? Any advice would be appreciated.

I am unfamiliar with a custom to go to mikveh in the ninth month. If there is such a custom, it has mystical, but not halachic sources. I wish you a healthy baby and an easy birth. Although sexual relations outside of marriage are not allowed in halacha, this is a transgression like any other which is atoned by teshuva, repentance. The best way to acomplish this is to decide ona Torah lifestyle for your self and the baby. We do not observe the laws of tumah in our times, we are all tamei to some extent. We do observe the demands of the halacha. The requirement to strive for holkiness applies to all. It should be reached through joy and a feeling that HaShem is aways available if I approach Him with humility and honesty, and a sincere desire to do His will.