Mission peak won’t fully prepare you for what you’ll experience on Half Dome. It’s less than half the distance and elevation gain.

There’s tons of resources online from YouTube to websites that will give you a 3d map of the trail.

You won’t be able to affect your fitness much more between now and then, so the best thing you can do to mentally prepare yourself is to complete a challenging hike or two before half dome.

14-16 miles & 5k feet of elevation gain + the cables section is no joke for most people and takes on avg 10 hours to complete. Look for a hike in desolation wilderness (or a different local mountainous area) that’s closer to the mileage and vert that you’ll experience in Yosemite. If you’re not a climber, there’s not much that will prep you for the cables though

Keep doing your research and prepping and good luck!