Yeah, Vinnie's a better name for a bull calf!
(I can talk, I had a buck rabbit called Lulu.
)
Lambs' nuts take more than 3 weeks to fall off, don't they? More like 5 or 6? And a bull calf's wee sack is a bit larger than a lamb's - I take it he won't stand still for you to have a good look and make sure the ring's still there.
If there has been a problem and the ring hasn't worked, you can use the burdizzo up to 3 months old. If you haven't burdizzoed before, definitely get someone who knows what they're doing to show you and help you - if you do it right it doesn't hurt them and works, but it's really easy to not do it right and either cause quite a bit of pain and/or end up with a bull.
Otherwise, castration by the vet is very quick and painless at the time of cutting; they can be a bit miserable for a couple of days afterwards but it is only that - a bit sore for a couple of days.