Uh, yeah not CR 3. It's fast, has reach, and averages 46 damage per round with successful hits. With that Strength and a normal proficiency it will hit more often than most players. The low AC and what 64 HP? that will help them take it down quickly.

Still, it's damage is pretty impressive. It's saves are pretty difficult. Looks like you're giving it a +3 proficiency so it's attack will be a +9. That's super high. Most PCs at lvl 3 in my game have an AC of 15 or 16. A few levels higher it might raise by a bit, but +9 will still hit more often than not. You need an AC of 20 to make it 50%.

Also, bite should have the strength bonus to damage. Why isn't multi-attack including bite as an option, is that mostly reserved for opportunity attacks or?