[Michael Romanos]

Timid dogs are uselss at agility. So he is not timid as you say.
Here are a couple or so of quick suggestions:
Go back to taking him around the course or over or through the obstacles on-leash ie you control him through the leash so when you say GO, he goes.
Do this many times - even (and especially) if it is only jumping a single hurdle.

Do the pep talk beforehand like I said in another post ie get down on your knees with him at the very start of his entry into an 'event,' get behind him, gently raise him up off his front legs, scratch his chest and tummy and tell him excitedly that he has to run his fastest and perform his bestest, then line him up right alongside you and both race at the command LETS GO.

Go back to the basic come, sit, stay training routines. Over and over.

Agility training should be fun for you and your Corgi - remember to make it fun, fun, fun and show lots of enthusiasm that can rub onto your Corgi, lots of praises and patting and treats and tugs of war(if he likes tugging).