Tekkit Legends Macintosh RAM allocation

[IHaveAProblem]

Im running a tekkit legends server on mac and in all my tekkit and other wise servers I've used the following command file to run the server:

#!/bin/bash
cd "$(dirname "$0")"
exec java -Xms3G -Xmx4G -jar TekkitLegends.jar

At the moment this command it not working, the server will crash immediately

The server is able to run if I simply open the TekkitLegends.jar file but it runs very slowly because it doesnt have enough RAM. Is there an alternative command I should use or another way to allocate memory to the server? I would appreciate help so much, and thank you in advance

 

[Side note- I have also tried 

#!/bin/bash
cd "$(dirname "$0")"
exec java -Xmx2G -Xms1G -XX:MaxPermSize=128m -jar "TekkitLegends.jar" nogui

this is based on the start.bat file that unfortunately only works on PC.)