How are you saving your image? and when you say it is stretched do you mean in the c2 image editor or in your layout?
also as a side note its not that good to have that big of images it will take up alot of memory.its recommended to try to break up you image into smaller pieces if you can. with sprites/textures it is always good to remember gfx cards like images that are the power of two(128,256,512,1024 and so on). so your image when exported when be seen as 2048x256. that can make memory use go up quickly so here are some links that may help you
https://www.scirra.com/tutorials/577/co ... imisations
https://www.scirra.com/blog/112/remembe ... our-memory