My turtle wont bask or eat?

I got a yellow belly turtle on friday (its now monday) He was eating at the pet store but wont eat since ive got him home. I also havent seen him bask. i got a turtle dock and sometimes hell put half his body on the edge of the dock and hang off in the water but he wont go up under the light. He also spends alot of... show more I got a yellow belly turtle on friday (its now monday) He was eating at the pet store but wont eat since ive got him home. I also havent seen him bask. i got a turtle dock and sometimes hell put half his body on the edge of the dock and hang off in the water but he wont go up under the light. He also spends alot of time completely submerged in the water behind the filter.

what do i do?
Update: hes in a 10 gallon tank is that too small? hes a baby only about 3inches. lady at pet store said hed be ok in that until he gets bigger
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