I have tried the floatplane mission several times but when I land to pick up the passenger I always get stuck against the jetty and can't reverse out again. I looked on Google to find out how to reverse and it seems that you use shift + P, but whenever I use that key combination I am told that "the tug service is not available at this airport". Am I doing something really stupid or is there another way to go into reverse?Thanx in advance

Try approaching from the "side" of the dock. i.e. parallel to it. You need to be careful of your speed. I's easy to overshoot if you're not careful.Also, you can raise your float if you need to for clearance.