Don't give up! I had something similar to this happen a few years back on my first bow hunt. I had 4 does lined up at 20 yds and I went to draw back, couldn't, so I let it down and tried again and the arrow had unnocked and fell. It hit every metal step on the way down.
All I can say is keep going at it. This year I had a great hunt when a 4 pointer came at 15 yds. (from outta nowhere) and I had just enough time to get my bow, draw back, and whack him (while he a had a clear line of sight at me the whole time). I double lunged him and he didn't make it 40 yds. I like to get mad at myself and say to myself that if I don't get the deer, everyone is going to laugh at me, so in return I get the courage to draw back and bring the deer home with a good story. Hope this helped, good hunting