I’m trying to create a sidescroller game but it seems that my character is colliding with the wall to the left. And when I try to do a double jump to the other platform and my character barely made it, the platform is not colliding right.
Have your movement actuators apply linear velocity rather than using translation (Loc). You have the right idea with jumping, just apply that same motion to running.
If you change the Loc of an object, you are essentially ‘teleporting’ it with magic through space. Useful, but not in your case. You want your physics object to be moved with physics, not magic.