Based on my direct experience (self-employed, married filing jointly), you are not likely to be penalized. As you've noted, you are currently employed and you are currently having taxes withheld. The side gig is providing you additional income.
During the first year of filing that included self-employment taxes, I received a notice suggesting that I file on a quarterly basis, to avoid penalties. For that year, we received a refund and years hence. We have never again received a notice with the suggestion.
Anything you do to ensure that you are paying sufficient tax will prevent warnings or penalties. If you do not adjust the income withheld from regular employment and do not make quarterly payments, you may have to pay additional taxes, and may receive a warning.
This information is qualified and quantified in an IRS document online.
Penalty for Underpayment of Estimated Tax
If you didn’t pay enough tax throughout the year, either through
withholding or by making estimated tax payments, you may have to pay a
penalty for underpayment of estimated tax. Generally, most taxpayers
will avoid this penalty if they owe less than $1,000 in tax after
subtracting their withholdings and credits, or if they paid at least
90% of the tax for the current year, or 100% of the tax shown on the
return for the prior year, whichever is smaller. There are special
rules for farmers, fishermen, and certain higher income taxpayers.
Please refer to Publication 505, Tax Withholding and Estimated Tax,
for additional information.
"You may" does not mean you will be penalized. It is interesting to note that if you've paid one hundred percent of the tax due the previous year, you don't have to worry about a penalty.
