I got my new board delivered this week without the fins installed, I have followed the instructions online but the centre fin is not moving and is very tight. I have managed to get it in but it sitting a little further forward than I think I need it too and is not budging. Any advice - it's a fanatic diamond board.

It's a pretty common thing (I wouldn't call it a problem) and it's best to be a bit tight than a bit loose.. If it's only a little bit off where you want it I'd recomend leaving it.. or pop into a local sup or surf shop and ask if they'd have a look at it for you.. Sometimes a rubber mallet is necessary but usually a firm wack with your palm will do the job.

Like DJ said, its good for it to be tight.

You can put some surfboard wax on the bottom sides of the fin to make
it go in easier and for it to be easier to move around. This will probably
do the trick unless it is super super tight, but you already got it in once,
so the wax should do the trick.

If putting wax on it doesn't do it, you can sand the sides down slightly
with sand paper or a flat file.

Sometimes I use a rubber mallet but you want to make sure your fin box
can take it - not sure about your particular board.

There is a video of Jimmy Lewis cranking a mallet on a fin.

Thanks for the advice it's tracking quite well at the moment but will pop it into the surf shop I think. But surprised at how much force was needed to get the fin in to be honest so it is super tight.

Watch this.....