Your 1099-R, Box 7, must have code of 4, to claim the 10% death exception.
You will need to contact the firm that issued your 1099-R for a correction.
You will be taxed on the distribution but should be able to avoid the 10% penalty.
The following article from Fidelity is very beneficial for non-spouse inherits of retirement accounts:
https://www.fidelity.com/viewpoints/retirement/non-spouse-IRA
