Don’t worry about it. No one will give you any crap. Just make sure you’re off on the right so you don’t block someone whose still spinning up the hill in a low granny. This year’s one of the flatter rides so you should be good to go.
If you’re concerned about not riding all the way up, stop when you’re half way there, take the stress off your legs, catch your wind, get your camera out and take a picture of those climbing or walking the hill behind you, drink some water, put your bike in a lower gear and then get back on your bike and try to make it to the top. Put some music on (I would recommend Areatha Franklin) and get your cadence in beat and zone out till you reach the top. You’d be surprised at what a short break and good cadence tunes do for getting you back in the saddle and up the hill.
If you’re still too pooped to pump, then walk the rest of the way. Like I said, no one will give you any crap. You’re doing RAGBRAI and you’ll be riding your bike 7 days for nearly 450 miles! I’m 62 and this is my 30th RAGBRAI. You’ll be enduring sun, hunger, sleep deprivation, sore butt, aching thighs for a whole week. Nobody should be able to give you any crap about whether you walk or ride a hill. Everybody walks a hill sometime or other. Ask anyone who was on RAGBRAI in 2010 about Potter’s Hill.