Strange Flinging

I was trying to dock two spacecraft together, both were very small, single engine craft. When they were about 2km away, I used a burn to try to align the two craft. When the burn finished, I hit m to check their orbits, and when I did my craft immediately slammed into the nearby planet. I don't what could have caused this. Now the remains of my craft appear to be in the center of the planet, as I can see clouds, space, and strange white squares.