JPEG problems

Dear Professionals

I am an artist that painted a large scale work - 200cm x 140cm.

I took photographs of this work. They are JPEG. I dont know much about this.

Anyway I then manipulated the photos digitally using GIMP2.

Now I have a very good market for m work yet took it to a printer that claims the image resolution is too small as is dpi.

How can I solve this? I am trying to blow up a digitally created imagenot a photograph of an image. So I need to reproduce the image to 200cm x 140cm and canvas ink print it at 300dpi at least. Surely this is possible?

please help if there are any GMP users / experts out there your help would be much appreciated.

thanks kindly