My bike is "leaning" a lot...

Check wheels are true.
Check rear wheel is centred properly in the track ends.
Check stem is adjusted correctly so that the bars are perpendicular to the forks.

Edit: How much is a lot?

Wheels are brand new so they are true (I hope).
The rear wheel is pretty much centered.
The stem and fork looks perpendicular to the forks.

But I'n not sure if the fork is 100% straight. How do I check the alignment of the front and rear wheel easiest?

Wel a lot is almost as much as it's impossible to ride it without the hands on the bar. 10 degrees maybe? I dont know?