Yes if you didn't get the Advance you would get the whole credit on your tax return. But you already got half so you aren't losing anything.
I found this in a news article, it explains it pretty well........
While the CTC expansion was structured to not increase taxes on any household, a dollar of credit received in advance results in a dollar less received at filing time. For families unaware of the trade-off, it could mean a surprise when they see their refund total this year.
Consider a married couple with a 10-year-old child who normally received their $2,000 CTC when they filed their taxes. They would have received $1,500 of their $3,000 in advance. As such, they could potentially see their refund shrink by $500 even though their total benefit increased to $3,000 because they are left with $1,500 instead of their normal $2,000 at tax time.
