macOS Any gnuplotters?

[Big Dave]

I am new to gnuplot. I am trying to clean up my plots. I am having trouble with my color legend. The bar marks separating the values don't line up well. The X axis values are congested too. In any case, if you can offer suggestions, I would appreciate it. My gnuplot script is:

#!/usr/local/bin/gnuplot
reset
set terminal postscript color solid "Arial" 12
set font "/Library/fonts/Arial.ttf"
set xlabel "This is the X label " font "Arial, 18"
set title " This is the title " font "Arial, 18"
set ylabel " This is the Y label " font "Arial, 18"
set xrange [-100:100]
set yrange [-100:100]
set xtics (-100, -90, -80, -70, -60, -50, -40, -30, -20, -10, 0, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100)
set ytics (-100, -90, -80, -70, -60, -50, -40, -30, -20, -10, 0, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100)
unset key
set size square
set view map
set colorbox
set palette model RGB maxcolors 10
set palette model RGB defined (0 "#0000FE", 1 "#5600E2", 2 "#6C5EE2", 3 "#00FEFE", 4 "#80FE96", 5 "#00FE00", 6 "#FEFE00", 7 "#FEA820", 8 "#FE74FE", 9 "#FE0000")
set cbrange [0:9]
bind Escape "exit";
set out "output.ps"
splot "data" u 1:2:3:4 w points pt 5 ps 1 palette

my data file named "data" contains the following:
50.00 0.00 0 0
35.36 35.36 0 1
0.00 50.00 0 2
-35.36 35.36 0 3
-50.00 0.00 0 4
-35.36 -35.36 0 5
-0.00 -50.00 0 6
35.36 -35.36 0 7