Hello, welcome to BW forums and congratulations on the birth of your new baby
New borns really do sleep a lot. I would make the most of it while you can!! Soon enough he will be awake more and you'll be trying to find time to have a shower or grab a bite to eat.
It might be that you could have more luck waking him at a slightly different phase of his sleep, so maybe try 2.5hrs rather than 3 or try 2hr 50 even - if you can catch a lighter phase of sleep he might be more willing to feed even if he is still sleepy. You can also continue to try to dream feed (usually at night but if you want to try in the day as he is sleeping so much then you can do that too).
I would probably not let him sleep longer than 3hrs, which makes the milk feed times more like 4hrs apart rather than 3hrs apart, but then if he wakes and it has been less than 3hrs I would probably feed then too so that you can catch him whilst he is awake - if it has been 2 or 2.5hrs since his last feed say, don't worry about stretching him right up to the 3hr mark. This might make it easier for you and ensure he has enough feeds across the day/night.
And as he is sleeping so well right now use your time wisely
Get rest. Get fed. Get showered...