My thoughts as well. In my old tinny for fun one day we tried sticking in a piece of wood to see how it would affect the performance of the boat. Gained about 3 mph but noticed it seemed to look like the transom was being stressed, pulled the wood out. This was with an old 2 stroke on a 14ft tinny and it wasn't sitting as high as your motor is. With the height of your motor (clamps seem to be right at the top of the transom) and the weight of the 4 stroke, it appears to have stressed (warped) the transom.
First, I'd take the boat in and have it repaired, might be a very serious problem if left unattended. Second, I'd get rid of the wood and get the motor sitting lower. 3rd, check the weight rating for the motor on the boat. The horsepower may be fine but you might be exceeding the motor weight rated for your boat. I'm certainly no expert at this and these are just my observations.