I have an 8D that was made about 6 years ago. This is my first year in college so I have been playing A LOT. I have noticed that my thumb wraps around the trigger because it is so small( the trigger, not my thumb) and my thumb has been getting bruised. I have a big hand so its not even like i could pull my hand back. Is there any extension I could get put onto the trigger to make it wider? Or should i just get a dime and put it on?

The dime thing I always thought of as extending the levers for smaller hands. I do not think the dime would help your situation. Also, Conn 8D's are known to have large reaches and most people complain about it being too large.

Before soldering or glueing anything onto your horn I would suggest checking that your valve height and hand positions are correct. Are your finger levers adjusted as high as they can be? And if your 8D was made 6 years ago can we assume it is a string linkage? If so, is it adjusted to the maximum? Finally finger position: are your finger in line with the finger levers?

The finger should be in line with the levers, this will bring your thumb back farther into the correct position. If everythign above is done then try having a ducks foot installed. Talk to your repair person about installation of the ducks foot. Have your teacher check your hand position. If it is incorrect you can sustain injuries, including carpel tunnel.

If adjustments are needed you want them done correctly without damaging the horn. It is absolutely worth having a professional repair person install a strap or ducks foot correctly. Balancing the horn correctly will make a huge difference in your ability to play.