GPS tracking gives me wrong path

I am having trouble collecting GPS coordinates. In my case, I need to walk from point A to point B and collect the coordinates avoiding any obstacles. I used an android phone and mapmyrun app. When I start from point A, I can see it does not start from where I am standing. It shows I am at the other side of the road. While walking along the footpath sometimes the GPS takes me other side of the road and shows my location in a restaurant or in a building whereas I am walking in the footpath. Now I have the coordinates of these walks. How can I remove these errors from the coordinates?

Note I also used other apps like adidas Runtastic. It gives me same problem. The GPS location changes a lot.