You do not get in trouble for not claiming your son, but you might miss out on tax credits.
If you have already filed your return then you will need to see if your return gets accepted or rejected before you can add your son on your return.
The 1040X form for 2019 hasn't been approved yet by IRS. Please, keep checking the following information below on how to amend your return; it will be updated once the 2019 form is released. Currently, the form is scheduled to be released on 02/20/2020.