First, you are conflating mortality rate with case fatality rate (CFR). Mortality rate is deaths with respect to a total population; CFR is deaths with respect to diagnosed cases.
Second, since this is an ongoing outbreak the CFR is a moving target. Your calculation assumes the ratio of deaths to recoveries remains what it is now for the ~40k active cases. However, the CFR by that calculation has been steadily falling. Additionally, since CFR is only based on diagnosed cases the struggles with testing capacity, particularly in the US, will distort it by biasing diagnoses towards more severe cases.
