If you eat your burrito over a tortilla, anything that falls out will simply start building your next burrito!
The first rule of chess club; Hide from fight club.
"As soon as Aragorn and Théoden have left the Fate
Track, the Free Peoples player can flip Recruitment
tokens in Recruitment Areas using a Muster Action
Die (or an Action token), just as if they were in a
normal Region: For example, flipping one token
in each of the two Areas, or flipping one token in a
Recruitment Area and one token in a Settlement." (Gondor scenario rules, p. 31)
In our last game Theoden entered play quickly but with only 3 riders.
I was badly in need for more units - is it correct that I could not flip more Recruitment tokens with a Muster Action Die before Aragorn entered play?
That is correct. When Theoden enters you'll flip all of the tokens but any that are subsequently added cannot be flipped until after Aragorn arrives.
3 Riders seems unusually low. How did you manage that?