Epson 2750 set up

Hi guys a couple of moths a go i decided to start selling t shirts online, i sell them on etsy , to be more specific, when i started i was going to school and i did not have much time to do the designs and print the t shirts, so i went with the print on demand option, now that am done with schools i want to start printing the t shirts myself, am just a designer and i dont know much about the t shirt printing business, so i bought an epson 2750 printer inkjet with pigment ink and for the last coupes of days i have been trying to figure out but my printer doesnt printer doesn't print on any color of my designs, not even black and white, its just like a yellowish ugly color, i use gimp and inkscape, can someone tell me what am i doing wrong, is this issue has to to be fixed in the printer or the software ?

thank you