Matching client's foundation

Hi, sorry if it's long. This is really getting me down.

I'm pretty new to the make up world (just under 2 years) I've done various courses and learnt a lot although I know we are always learning & improving.
I've worked on a few clients, mainly friends and family.
But I'm really struggling with confidence when It comes to matching clients foundations.

I don't know what my problem is but it's putting me off of advertising for new clients and really getting me down.
I've got all my kit,...

Matching client's foundation