I think you did a stand up job tracking. Way too many hunters quickly give up. I don't blame you for feeling down over the experience. but you learned a huge amount with that. It sounds like one thing you don't need lessons in is tracking. For next season, as others have pointed out, bone up on your deer anatomy, and your shooting. I am guessing your 30-30 has open sites? With practice, you can become very capable a marksman. Read up on a six oclock hold. You aren't sighting using the center of the front bead....that ends up covering a huge amount of your target. You use the very top edge of your front site...the fine line, as your point of impact aiminig point.
Sorry you lost the deer, it certainly is reason to be upset, but I think from your story, you were a very ethical and appropriate sportsman.
One other thing...I understand your hesitation with the 2nd shot....but another round behind the shoulder into the boilermaker shouldn't harm much meat.