Trouble with 1" nipple onto 1" 200 psi poly tubing

I'm having a little trouble trying to fit a 1" brass nipple onto my 200 psi poly tubing. Is it ok to heat up the poly tubing with a torch to get the fitting on? The tubing is blue on the outside and white on the inside. If heating is ok, should I heat both the outside and inside of the poly tubing?

I use a heat gun and make it just hot enough that it still takes effort to get it on.

Agreed - and good effort. If it gets too hot it de-cross links and later you get a lost pump. Hot water is best, but even a hair dryer will work. Use GOOD clamps, 3 and install them while its still warm - retorque them a bit later with a nut driver, not a screwdriver.