I am not a fan of a heart rate monitor. Of course, you may like it. In fact, I don't like data at all, except for mileage, cadence, average speed. I judge my work using RPE, but I've been exercising a long time, so I know when I am going to blow up and when I am not working hard enough. And remember, heart rate ranges vary widely. My heart rate has always been higher than others when I am exerting myself, but my resting HR is low. I am not out of shape, it's always been like this.
You'll be fine. August is doable.