Third round stimulus reduced my refund even though it says i didn't get enough and am eligible for a credit. Why?

How much is on line 30?   Is it the 1390?  Line 30 is any extra credit you are getting.   Turbo Tax started out giving you the full amount so your refund was too high.   Then when you enter what you already got it is subtracted.  

Sounds like your total should be 2800 for 2 people or married.  You got 1410 giving you 1390 more on line 30.   Although 1410 is an odd amount.  The 3rd Stimulus payment is 1400 per person.  

The refund is only determined once you have entered everything on your tax return. While you are still entering information, the refund is only a temporary indication.

Before you entered the amount of stimulus received, the program had already attributed the stimulus amount and this is why your refund is decreased by the amount you received when you entered it.