Does Blue Sentinel give you an additional point off holding with his double hold effect at a battlefield?

No, Blue Sentinel does not give you an additional point for holding a battlefield.

According to RiftJudge FAQ #9539 and the card's ability text, Blue Sentinel's effect allows your "hold effects" to trigger an additional time. These hold effects—such as drawing a card from Grove of the God-Willow or adding [A] to your Rune Pool from the Sentinel itself—are triggered abilities that occur after you have already scored the Victory Point for holding.

Furthermore, Rule 465 of the Core Rules states that "A player may only Score, from either method, once per Battlefield per turn." The Victory Point is gained as a result of the act of holding; Blue Sentinel modifies the triggered abilities that happen in response to that score, not the score itself.