Wilting pussy willow?

 Hello, newbie here so bear with me!

I planted a new Japanese pink pussy willow a 2-3 weeks back, and it looks like it is struggling already. Some of the leaves have shriveled, and some have turned yellow. Affected leaves seem to be on the same  branches, with some branches unaffected. Seems to be younger leaves/ this that are most affected.

The soil was refreshed prior to planting, and there is an irrigation drip feed near it, and I think the soil is most enough. I was wondering if it was caused by being scorched (it was the boiling hot weekend when it went in); or if it got damaged in the post (i ordered it from crocus and yodel messed up meaning it didnt get delivered until another day).

Has anyone got any other thoughts on cause, or any suggestions on how to perk it up again?

Thanks in advance!