How to balance references in new acmart.cls format?

Hi I’m trying to balance the last page of my paper. It contains only references formatted with the new acmart.cls formt, and takes up about 1/4 of the left column. I’ve already tried a few methods:

usepackage{balance} 
balance 

and

usepackage{flushend}

and

usepackage{multicol} 
begin{multicols}{x}

None of these are working. The first two produce no change, and the last completely destroys the formatting. Does anyone know what the problem could be?