I am surprised that you got anything. The <TFT.h> library is for 128x160 ST7735 displays. I presume that your 240x320 has got an ILI9341.
Since you have bought a genuine Adafruit display, why not use the genuine Adafruit examples that come with the Adafruit library(s) ?
Incidentally, I ran your program on a real ST7735 display. It displayed the dog, but the colours were wrong.
When you are happy with the Adafruit libraries, we can show you some other libraries.
But I would definitely start with Adafruit.
Oh, and when you are running ok, it will be interesting to see if you actually have an ILI9340C or an ILI9341 controller. Don't worry. The 9340 and 9341 are almost identical.
David.