If it was in/for the correct year (i.e. in 2018 for 20018), you should be safe.

If you feel that you missed the deadline due to a reasonable cause, you may ask the IRS to waive the 50% excise tax. The request for waiver may be included in a letter of explanation, which you attach to your tax return (Form 1040) along with your Form 5329. When requesting a waiver, do not pay the excess accumulation penalty up front.

Most important: Complete Part VIII of the Form 5329

• On line 50, enter the amount of the required minimum distributions that were supposed to have been taken during that particular year.
• On line 51, enter the total of distributions actually taken during the applicable year.
• On line 52, enter "zero," and write "RC" in the margin. Do not enter the amount of the shortfall - even though it appears that you should enter on this line the amount you failed to take, you are supposed to put zero on this line if you are requesting a waiver of the penalty. If you put any dollar amount on this line, the IRS computers will automatically assess the penalty.
• On line 53 (amount of penalty), enter zero.
• Attach a statement to the Form 5329 indicating the reasonable cause and also verifying that you have remedied the shortfall and attach a photocopy of your distribution check, if possible.

If the IRS does not honor your waiver request, you will be notified.