It hurts a lot. When you win a battle, your points are calculates as 25 - (number of stars on your hand)
On an average, your hand will have something like 19 stars, so you will get 6 points for a win. The other points are from winning rounds. You will get 3 points maximum when a 5 stars wins a round, while someone can get 5 points from beating a 5 stars card with a 3 starred one.
37* deck is somewhat insane if you want to score well. A lot of people will tell you that you have to use 26 stars. That's patently wrong; however, you should use as few stars as you need to win consistently. If you can only win reliably with 30 stars, play that for awhile as you get better at predicting moves and doing the pill math. Drop more stars when you buy new/stronger cards that make playing with fewer possible or you feel more confident in your game.