On two occasions while sailing, the dory wasn't super responsive turning port (both occasions on port tack). 

I'm a beginner sailor, but one of the two times I was with my neighbor who is a very experienced sailor and he found it odd. 

I'm wondering why this happened. 

I have two guesses:

1- My rudder is not low enough (the bottom is current sitting three finger atop from the skeg) 

2 - My centerboard is not completely straight. 

Any suggestion?