You have answered yourself
2nd year worth 25% of entire grade and 3rd year worth 75% so if you put in a decent year three result not only could you secure a 2:2 you could actually still secure a 2:1
To secure a 2:1 you need an overall grade of 60% - 69%
You got 46% in year two so that would mean you were circa 14% shy of a 2:1 grade in year two so would need to score just shy of 65% in Year 3 to now obtain a 2:1.
You just need to work that bit harder in Year 3 (5% harder) to get the better final result,
Not sure what your degree is on but clearly maths isn't your strong point.
Good Luck