Open up the hide and the smell will tell you. If it stinks it has begun to decompose. It will also be a little blue or green on the flesh side. It is too late to tan it for hair on. You can still make it into leather.
If you unroll it and it just looks dry, it may still be fine. Air dried Elk and Deer hides have a lower chance of turning out alright.
Either way, next time you need to pack a little salt with you when you go hunting. 5 lbs or so. After skinning out the elk throw the salt on the hide and roll it up for the trip back. This will give you the best chance for a beautiful hair-on hide.