My birth certificate has my first and last name only but my s.s card has my first name and last name but it also has my moms last name as my middle name. I never use it but I don't know if it's easier for me to put on my birth cert. Her last name as my middle name or should I just take it off my s.s. Card? But what if I get married soon and want to change my last name. Should I wait or what should I do ?

I see no point in bothering to change any of these documents, yet. If/when you get married, you will start the name change process with your ss card - at that point you will need to decide (once and for all) what your new legal name will be. Then once you have your new ss card, you can use it as proof to change your drivers license and passport. Meanwhile your birth certificate simply remains as is, with your name as your mother specified when you were born.