what can I do so that my gum paste can be non crackly? Can I fix it?
Welcome to Cake Central.
Unfortunately, if it has dried to a 'crust' that portion is wasted. You can sometimes peel off the dry outside and use the inside.
To store gumpaste and fondant it helps to rub the outside with a bit of shortening, wrap it tightly in plastic and then seal it in an airtight container. You cannot be too carefuly wrapping this stuff for storage.
Last time this happened to me I tried microwaving it for a few seconds and it became soft enough for me to knead some crisco into it and somehow it worked. If you microwave it a little more it melts though so be careful to do it few seconds at a time.