Hi Dyson Sphere,
That's a good basis, but it can be improved.
First of all, I suggest that you have a look at the tutorial dedicated to the Voyager quest:
Voyager quest: tutorial
Regarding the rocket iself, the engines are well chosen, but I would remove one stage: just remove the third stage and give its fuel to the second stage. A second stage with a Valiant and around 40 tons of fuel is quite adapted to this mission.
Then, second advice, use everything you can. By the rules, your launcher can weigh up to 265 tons. Look at your launcher, you are 35 tons below the limit! Add some fuel to the boosters and the first stage.
Also, be careful to your trajectory when you burn from LEO: it looks like you tried to go to Mercury, you wasted a lot of energy! You have to plan your burn so that your probe escapes the solar system instead. There's a whole section of the tutorial covering that part, I let you have a look at it. There's also a video as a demonstration, don't hesitate to look at it to see how to do it.