You should be fine. You can’t book.
If you are catching it at Kirkby Stephen (as I and most others do), you are pretty much first in the queue as far as cyclists trying to get their bikes on. So that helps. I normally find it pretty empty.
I have only had one instance (try to catch it at Horton, further down the line) where I was refused. Most other conductors I’ve encountered pay no heed unless you’re being a dick and blocking the aisle with it.
Identify the ‘bikes’ strip above the relevant door and make an effort to be there as the train comes to a halt. In the spirit of asking forgiveness rather than permission, just heave your bike on in a cheery manner. You can easily get three in the two slots on the normal carriages, and I’ve stood with the bike vertically propped in the RH doorwell before with no problems.
PS If you’re having supper in KS, leave enough time to get up the hill to the station. It’s a mile (and quite steep in places!)