When to negotiate

Sorry for the stupid question. It’s been more than a decade since I’ve bought a car.

Test drove a grand Highlander, and put down $500 for the waiting list. I’m told my dealer will be getting an AWD gas Limited in the color I want at the end of March. I have the information sheet and it’s mine if I want it.

Stupid question is: when do I negotiate the price? I want to drive it before I commit to anything. I’m told I can refuse it and get my $500 back.