There are many ways to calm down a racing mind, and you are on the right track when you look to consciously control your thoughts. I would suggest this exercise to help you achieve a certain sense of calm.
Find something small and detailed that you can look at such as a coin or a pebble with many lines on it.

Hold it inbetween your forefinger and thumb and look at it. Really look at it, but do not study it.

Then when you feel like you are ready to start, breathe in for 3 seconds, hold your breath for three seconds, then take three seconds to release your breath, and hold your lungs empty for three seconds. Repeat this box of breathing with 3 seconds on each side while looking at your item.

You can let your mind wander, but when you feel it start to race ahead of you, just bring it back to counting your breathing and maintain eye fixation on your object.

This is actually a technique used in meditation, though we have similar techniques in hypnosis, and it can help you to calm your thoughts.