Eventually, it will all end up somewhat mixed together... it is really hard to keep it separated completely. However it looks pretty good right now.
1 suggestion: when aquascaping, try not to make things symmetrical. It looks more natural if it is not symmetrical. So, the tank looks like it is divided half and half... maybe just do 1/3 sand and 2/3 gravel, or visa versa. Also, it would help to soften the dividing line a bit... it is a little to straight imo atm.