The 1099 K will only include transactions done through a payment settlement entity for processing credit cards or third party transactions, therefore, yes, you will need to also add an entry for income that you received via cash and checks when entering your self-employment income. See the steps and sample screenshot below:
If your self-employment income was only from cash,
personal checks, credit card payments, or cryptocurrency
Type Schedule C in the Search box and then select
the Jump to link. This will take you to
where you can enter any cash, personal checks, credit card payments, or
cryptocurrency (Form 1099-K) related to your self-employment. You may
first be asked some general questions about your business. After you answer
them, you’ll be taken to the Let's enter the
income for (your line of work) screen where you can enter this income as
Other self-employed Income.