Tight gudgeon (wrist) pin

I have put both the pistons on the con rods but the drive side one seems very stiff. I took the piston off again and oiled everything before putting it all back together but it still seems a lot tighter than the timing side piston that flops from back to front freely.

I cannot see what could possibly be wrong as both pistons were marked for each side before being dismantled.

Any advice would be helpful before I put the barrels back on.

I'd check that you haven't damaged the small end bush during the rebuild. There may be a burr on the edge of it or a scratch on the inside of the bush.
Take the piston off again ( new circlip needed now) and try inserting the gudgeon pin without the piston, through the conrod. Try it from left and from right to see where it gets tight. If it's a small burr, you may be able to remove it with a scraper, or file.

Took piston off again. Cleaned everything but the pin was still tight in the middle. was fine at the edges but tight in the middle. I just kept adding more oil and eventually the pin seemed to free off.

I put the piston back on it seems to move fine now. I put new circlips in but forgot to check that one of them was sharp edge outwards. Will this make a big difference as I don't have any more circlips to use if I remove the one I have fitted?

You should be able to see if it's in the right way round with a magnifying glass. You can see on the ears of the circlip which way round it is.
As for what to do of it's the wrong way, I'd put a new one in, even if you have to wait to get it. Having said that, the Norton style ones are better than the wire ones for re use. It probably won't matter if you take it out and turn it around, but for the price of a circlip....