Mark’s Down On Your Syntax said:

Good point, Val. To reinforce that you could also say that Luke was planing to use the Force until the mind trick didn’t work on Jabba. By trying and apparently failing he would’ve appeared to be weaker. Using his abilities in view of everybody to kill the Rancor would’ve lost him that advantage. He was deliberately playing down how powerful he was until the Sarlaac and Jabba was mocking him for being a Jedi right up to that point.

If I remember correctly, in the movie he advises Jabba to not underestimate his powers. I don’t see him playing down at all.