2021 child tax credit please help

Hello - very confused on how to do the 2021 child tax credit. Everywhere I read says it is $3,000 per child under 18 and fully refundable. I only made $4,328 in 2021 and have two kinds under 18 yet I am doing the 8812 paperwork and coming out with a refund of $0 or $2,638. The forms are tricky and has be using a separate Credit A and Line 5 worksheets. I thought this was an easy $3,000 per child. Can someone please help?