In times of leaving for a few days, i set the tree in a partly shaded spot, put a saucer underneath and leave that full. Also, think about a different soil mix with some additional organic matter to retain some water for a longer period. I started mixing a small amount of peat with my previous 100% 8822 DE to help retain some moisture and it seems to work great.
Learn and try again!! At least you knew to keep it outside... thats a step above most of the other newcomers that ask if their tree is dead or not.