Retirement tax questions

I finished doing my 2020 taxes on Turbo tax Deluxe and was had put in information for 2 of my kids tuition 1098-T statements where I had paid over $2000 for each and was trying to get credit for the American Opportunity Tax Credit and it only gave me $500 for each instead of $2000 each. My AGI was $146000 which is under the $160000 mark to get full credit but apparently it added things to the AGI to make the MAGI like $175000. My question is where the additions came from??? I read the possible things that could be added back to make the MAGI and I didn't have any of those items listed.  I just want some clarification on why the MAGI is like $30000 higher than my AGI??