Rounding corners of UIModalPresentationFormSheet

forgive me if this is an obvious question i am relatively new.

I have a modal view which i set up with a custom size and rounded corners:

- (void)viewWillLayoutSubviews{

    [super viewWillLayoutSubviews];
    self.view.superview.bounds = CGRectMake(0, 0, 600, 450);
    self.view.layer.cornerRadius  = 60.0;  
}

However i find that when i round the view corners, i get this greyish colour appear on the edges of it (as if theres something else behind it) : (see picture).

How do i remove these greyish edges so it shows the background content like normal? I've tried adding

self.view.layer.masksToBounds = YES;

however this still gives the same effect as above.

Thanks,

- (void)viewWillLayoutSubviews
{
    [super viewWillLayoutSubviews];
    self.view.superview.bounds = CGRectMake(0, 0, 600, 450);
    self.view.superview.layer.cornerRadius  = 60.0;   
    self.view.superview.layer.masksToBounds = YES;  
}

I think you should set corner radius of the superView.