remove OR CHOICE=4 at the start of the loop then anything entered that is not 1, 2,3 will cause the loop to exit.
also might I suggest that you try to use only one variable as a flag for your loop; instead of DOWHILE Choice=1 OR CHOICE=2 OR CHOICE=3 OR CHOICE=4
try only Choice NOT= 4. I'm not sure of the syntax since I don't think I've ever seen this language before but I hope you get the idea. btw using a negative flag can be a bit complicated but i would try it in this case.
Good luck
"I don't believe in astrology; I'm a Capricorn and we're skeptical."