I honestly don't think anything is wrong with your actual picture but IG itself doesn't show them in high res. They already fixed the high res issue where it wouldn't upload your picture on using the S4. I notice this on IG period that images even of others that I am looking at that I know who takes high res photos aren't looking high res. When I look at that same image on an iPhone or my iPod it looks just fine on IG.
Also, I have a Black Mist Sprint Galaxy S4 for bid. Currently and only at $300 so far. Excellent condition. Lovely phone but it's not for me.. Check my signature.
Nexus 5 White