How do I add my sister to my deed but still keep me on also

You need to file a quit claim deed trasnferring ownsership from you to you and your sister. There is a sticky note at the top of this forum that explains the process.

Please note that what you are actually doing is selling an interest in the property to your sister. This action may have consequences if there is an outstanding mortgage and there will also be tax consequences.

Also keep in mind that a deed takes precedence over other legal documents. (such as a will) If you later wish to remove your sister, you will need her permission.