I almost want to say a whole bale is too much for one baby. Also transitioning from straight alfalfa to a grass hay can be tough as bunnies will prefer the alfalfa. What kind of pellets is your bunny on? Usually young rabbit diets with have an alfalfa base so the additional is not necessary. I don't know just my opinion?
The only good pellets I am able to buy are the natural science adult rabbit food from oxbow. And he is eating Timothy hay right now but it's almost gone. And I am getting another baby bunny in 7 weeks.
Alfalfa is fine up until the age of 6 months and then they should be eating a timothy hay or similar blend.
I would get a much smaller amount of alfalfa and not an entire bale. Perhaps ask the people at the feed store if they have separated flakes or loose bits that came off a big bale that you can have?