When you are citing three authors in-text in an APA paper, you can include et al. However, in the reference list, when citing three authors, you include the last names and initials of all three and an ampersand (&) symbol.
An in-text citation in APA for three authors looks like: (Brown et al.).
A reference list citation for three authors looks like: Brown, J., Barret, T., & Kelly, D.