ArrayFunction changing multiple cells in Google Sheets

I’m making a calculator and want to make a function to let the user know “Hey, don’t use more than one checkbox in this column” (I don’t wanna touch scripting as the last time I used it it broke a lot of things), and am using the ArrayFunction to allow me to make sure there is at least one checkbox in the column that is true.

=arrayformula(if(E4:E19=true,if(XOR(E4=true,xor(E5=true,xor(E6=true,xor(E7=true,xor(E8=true,xor(E9=true,xor(E10=true,xor(E11=true,xor(E12=true,xor(E13=true,xor(E14=true,xor(E15=true,xor(E16=true,xor(E17=true,xor(E18=true,E19=true))))))))))))))),"", "Too Many Gags!"),""))

When I have it trigger, however, it pops up in multiple cells, listing in whichever cells are checked. I want it to only appear in the cell below the checkboxes (in this case, E20).

I’m still fairly new to Google Sheets, so I’m probably missing something obvious.