Having an ADD button appear in your Gedcompare is not the same thing as ADDing the profile.
Click on the ADD button to open an Add Person form that will be pre-populated with information from your Gedcom, to create a new WIkiTree profile.
For best results with Gedcompare, I suggest that you start with someone in your Gedcom who is matched to a profile already in WikiTree. Use COMPARE to see which members of their immediate family still need to be added to WikiTree, then use ADD buttons to add the parents, spouses, children and siblings. When you are done with that little family, click another COMPARE button to branch off into the next generation or next family, and repeat the process.