Running in the morning, cooler weather, and the adrenaline of the race does help. It shaved +1 min off my first race!
I vowed then and there to increase some of my training runs as I averaged a faster pace for 13 miles than I was doing on short runs and even some short speed runs in training. You'll get there, just don't let doubt and frustration creep into your mind. You did not gain the weight in a few weeks, thus you will not lose it all in a few weeks. However, it does come off faster than it goes on. Patience my friend.