Hmm, maybe try a different grip. Many bowlers make the mistake of holding it with thier thumb, pointer finger, and middle. You actually should hold it with your pointer, middle, and ring finger. But if you still have a curve you can try to use it to your advantage by trying to find out here it curves, then maybe move to the opposite side and it might go to the middle

Well... when i try to flatten (make the ball go straight) the ball all i do is keep my hand straight. But what kind of ball do you have? If it is highly reactive it may help a little but not necesarily make it go totally straight.

just throw the ball straight

I would recommend a "Robbi" it is a wrist brace that will force your hand to stay straight instead of forcing your hand over top of the ball. In which case is a common mistake of bowlers. and the do not notice it.

usually u cant just make a curve go away unless you stop bowling for like 10 years lol

Try not to let your wrist bend and hold the ball not to tight,but not to losse,if you do your ball will Drop WHILE YOUR IN YOUR SWING if you do,it will be very bad!Good Luck!!!!