A 3 year old would feel bad about asking for a diaper change as by age 3 some kids are embarrassed about being in diapers or needing to be changed.
If your 3 year old is feeling bad about asking for a diaper change it could be a sign that your 3 year old is ready to use the toilet.
However if not then you should change the 3 year olds diaper without them needing to ask about it and do it in private such as in your bedroom, the 3 year olds bedroom etc.
3 year olds use diapers even when they develop the ability to hold it as they may not be emotionally ready to use the toilet.
Even when a 3 year old has bladder and bowel control it doesn't always mean that the 3 year old is ready fully for potty training and diapers will be needed for awhile until the child is ready.
Some kids don't train until 3 years and 6 months to 4 years old.
When a kid is ready fully to potty train the potty training should only take a few days to a week at most.
Eventually your child will be ready to use the toilet when they are ready and until then they should wear diapers.
Some kids may also wear diapers at 3 for bed wetting even though they are diaper free during the day which is also normal.
Many 3 year olds wear diapers and it's completely normal.
A 3 year old may also be more comfortable in their diapers and not like underwear.
Potty training your child before they are ready can lead to issues with their bladder and even bowels so it's also best to let the child decide when to potty train.
It's not considered late to be potty trained until the child is 5 years old.