HELP lol. I brought a Lavender Toscane yesterday and watered it in well

When you bought it, where was it? Inside? Under cover? And are your air temperatures currently pretty cool, specially at night? It might be shock from being under cover and then being left out all night in cool temperatures.

well in town there is a indoor market that sells them @ 2.99 and i brought mine on an outside stall at £1.

so it was outside but i dont no if they r the same stall.

um the weather is muggy, warm n cloudy.
at night its warm with like a cool feel so like a summery night nearly.

its pretty cool now and quite shady with clouds so ive gave it a drink and suppose will see how it goes.

Well, you don't know what happened to it before you bought it, I guess - hopefully it'll adjust and settle in, but plants sold on stalls are locked up overnight inside, so this is probably the first time poor little thing has been exposed to any temperatures under about 19 deg C.

It could be too much water or not enough.
If its roots are saturated it'll hate that and if it's not had enough water and it's getting sun from 9-4 it'll not have enough moisure reserves to cope with the heat from the sun - in this region we've had hot sunny spells amongst the rain and it's quite hot when it comes - that'd be enough to make it struggle.

Seeing the bark that the plant is 'in' makes me wonder if it should be someowhere where you're not trapping moisture into the soil.
Bark is used to help trap moisture and lavenders want the opposite conditions - impoverished soil in full sun.

All good points, Louise, but frankly, unlikely to be the problem if the plant wilted overnight, too soon for sitting in wet soil damage. Keep it watered as its in open ground, Sense19, while it establishes its water seeking roots for itself.