1099-R inherited Retirement upon death, am I double paying taxes?

- Mom contributed to a retirement account during her years of work
- She passed away, the account was transferred to my name as a Deferred Annuity, which I had to Cash Out or Rollover into an outside 401k/Roth within 3 years
- At the end of 3 years I chose Cash Out, and paid a very large amount in Federal Taxes
- I received a 1099-R from the company holding the Deferred Annuity, so how do I file this, as Box 7 = 7(Normal Distribution)? Having already paid taxes on cashing it from the account holder, will I be paying taxes again on this income?