130-140 bpm isn't really that fast; I would not worry about readings like that on a walk for me personally, bearing in mind that even a gentle run will likely be closer to 160+
You might want to find out your real max heart rate, I hear a "good" method is to sprint up and down a steep hill until you are exhausted, and see what it gets up to. It could be that your heart naturally beats a bit faster than the average
Congrats on getting a 305, I'm jealous
