It arrived already in very poor condition. It was sent in the mail, having probably been raised in a green house and got etiolated and mouldy on the journey. At that point it was still saveable. But then I’m afraid you did pretty much all the wrong things. You exposed it to full outdoor sun for 7 hours without hardening it off (3 hours on a windowsill is not hardening off. ) Then you disturbed the roots by repotting it and it doesn’t look as if it has been watered since. So much has gone wrong with it that I’d call it a day. Go to a garden centre and buy a new lavender which you can see before you buy it. If it was not bought from an outdoor source make sure you harden it off properly.

3 hours of hardening off before planting in full sun??..

moisten your potting media before use.. yours looks bone dry.. probably because you tried to water it after planting in it ...

get the media moist.. put in in full shade... and water it properly. and in 30 to 60 days. you will know if it survived... or it will be dead by then ...

there is nothing you can do.. to make it look good by tomorrow... just proper water and patience ...

ken