I rubbed off a raised mole and all that is left is a black spot . my derm told me that i should watch and monitor the area to see if it regrows but i feel uneasy about that because i fear if it's melanoma and it would spread without me knowing ?

Maybe your dermatologist knows that it was not a mole but another kind of bump and, the leftover pigment is just post inflammatory pigmentation. If indeed it was a mole that left pigment cells, you would see the dark spot as well and, you should monitor it. If you are concerned because you think the original bump was a melanoma, ask your Doctor to please biopsy the area of the “black spot”