I think that it is very important to practise drawing from an elevated platform. I do most of my practise from a sturdy metal folding chair. The muscles that are used to draw are different than those that are used to draw on the ground. I would suggest practising like that and you may find that you need to turn that bow down a good bit until you build up. On the other hand sounds like you had a great hunt, many go through many seasons and do not have such a fine animal within bow range. Maybe you should think about what you did right and realize that except for being overbowed that was a fine effort.