Yes thinning out would be a good idea. If you still have the seed packet it will probably tell you the distance apart the plants should be. If it doesn't, try about nine inches.

What kind of soil mix are they growing in? If a commercial multipurpose compost, as it appears, they may also need a gentle feeding. A half strength solution of fish emulsion and seaweed extract is one good treatment.

Thanks for the replies I will do that

Had another look at the photo - when you replace the netting tunnel after spacing them out it would be a good idea to space the hoops much further apart so the netting is level with the hoops, if you see what I mean. It shouldn't be sagging like that. If the tunnel is too long for your space its better to just bunch the hoops up at one end of the bed to keep the netting almost taut.