The 10% was most likely not enough.
Any taxable distribution from a pre-tax IRA will appear on Form 1040, Line 4b, (where it will increase your tax due)
The 10% that was withheld should appear on Form 1040, Line 25, (where it will reduce your tax due).
Once all the math is done, you end up actually paying the correct amount of tax.
Please note that the CARES act allows you to avoid the penalty for unqualified early withdrawal; not the tax itself. Many people are confused on this point.
