Have I ruined my new turf?

Brought a new build (June last year)
Had professional gardeners do the work. They said they layed really “good grass” and yes, it did look lovely all winter, until I decided to cut it yesterday. Now it looks a total mess. Yes - it was very long, but I don’t know if it was the old mower I was using? Or something else?
Do I know need to lay new grass seed, or will it come back with watering?

 

Hi @Lermzy34
Personally I think it will come good with a bit of watering. If it had got really long then I would have cut it in stages gradually working down to a shorter length, but not too short!!
Can't quite work out though what the dark , almost scorched like patches are...unless it's oil from your old mower

Someone will undoubtedly come along with a better reply ...I'm certain.

 

Just make sure the blades are sharp

 

As Jiffy and Upsydaisy have said. Make sure your blade is sharp, what make and model of Lawn mower is it ? You should be able to buy a new blade on Ebay or Amazon. I sharpen my blade once a year using an off hand grinder, making sure the blade is balanced after sharpening. Mow regularly and not too short, it's not a putting green
I would use liquid feed at first rather than granular. I like Vitax feed and weed applied with a watering can. Lots of lawn gurus on here for more detailed advice if needed.
I am not an expert, my front lawn is a disgrace after a winter attack of moss. My back lawn looks fine, but has two large holes in the middle dug by my cocker Molly, which she won't let me fill !