I dyed my hair, but it left some parts out. If I have more dye left over should I go back and fix the parts.

Yes, unless those parts are visibly brighter (e.g. more blond or very light brown) which would stop the dye properly setting into the hair (or changing its colour to something weird like pink or green).

Yeah it is just lighter at the top. I got the foam dye and it doesn't look like foam anymore, should I still use it.

If it doesn't look right anymore, don't use it. It's the same with most foods and other cosmetic products like shampoo or soap.

No don't use it if you've had it a while.

It's usually written on the box somewhere... throw away any un-used dye

You could buy a spray in one of the same colour,just temporarily.Use it on the places that you've missed.

There is also the non- permanent ones that last about 24 shampoos, there very good,if you can try and match the colour.

When you re-do your whole head you can then make sure that you cover the bits that you missed first time.

OK thanks I threw it out and I think it looked discolored because of the lighting in my bathroom.