Can I get married in an Islamic (Shiite) center? In this the only center in U.S.A available in my town.

Praise be to Allah, the Lord of the World; and may His blessings and peace be upon our Prophet Muhammad and upon all his Family and Companions.

Completing the marriage contract in an Islamic center even if it is a Sunni is not a condition for the validity of the marriage.
A marriage becomes valid when all the conditions and basic elements of Shari'a regarding it are met.
However, if you do not know the procedure for completing the marriage contract with the guardian of the girl, then it is better to seek help from a Sunni scholar or the one who has the knowledge from among Ahl-al-Sunnah to complete the marriage contract. Know again that the marriage contract does not need to be held in an Islamic center. We advise you so, because if you go to a center of Shi'ah not having the knowledge of conditions and basic elements of a valid marriage, it may cause you to commit what nullifies a marriage without being aware of that.
Allah knows best.