not enough starter for recipes

I am new to this business of baking, so others here may be able to provide more insight than me, but here are a few comments on your post that may be helpful:

1.  It sounds like you are using recipes that call for quite a bit of starter.  Most of the ones I use call for 1/8 cup.  A notable exception to that are some of the ones that I've used the starter more as a flavor addition than a yeast (e.g., pizza crust).

2.  Starter is exponential and can get as big as you want.  I feed at a 1:1 by weight ratio, typically feed so that my amount doubles roughly, and pour out what I don't need before feeding.

3.  I pour excess starter into another container that I keep in the fridge and use it for recipes like the pizza crust, that demand a lot of starter.  I'm banking on the fact that it doesn't matter so much if the starter is a bit older for these recipes-- in fact, if anything, it probably makes the starter even more sour since it hasn't been fed and is just festering there for a while eating up the remaining food and pooping out acetic/lactic acid or whatever its doing in there.

4. I keep my starter at about 1/4-1/2 cup which allows me to start a recipe pretty much whenever I feel like it.  My starter is pretty active, so I could probably get away with much less and just feed it 12-24 hours beforehand.  I feel ok with keeping a larger amount because I am not wasting the starter, since I save it for when I make pizza.

5. If you are going for this afternoon and you have an active starter, you could probably go for more than a double at the feeding stage and be ok.  Id watch out for overflow and make sure it completes the "eating" cycle before using it.  This will ensure a high yeast cell count.  There is also the option of adding less starter, which will add some time to your fermentation stage and result in a more-sour dough.

Man.  I talk too much.

Good Luck!

to merely doubling. You can triple, or sometimes even quadruple your starter, ie 1:3:3. Just be sure to let it get good and ripe before using. I still discard at least a small bit when doing this.

rather than discarding starter, which seems a waste of good ingredients, I bagan yesterday, adding the "discarded" starter to my regular yeast dough and ajusting the recipe accordingly.

I never throw out starter at all. My routine is to keep about 50 grams starter in the fridge, in a covered container. When I want to bake, I scrape the starter into a bowl and add 50 grams water and 50 grams flour, giving me 150 grams starter which I leave overnight. This is the basis of the dough.

To the now "empty" container I add 20 grams water and stir this about thoroughly, then tip it into a clean bowl  and stir in 30 grams flour and mix it then cover it. This is left for about 5 hours then put into the fridge - this is now my 50 grams starter which I keep until the next time I bake. 

This system has now been going for several years and it is a vigourous, energetic starter which makes a great loaf. And has the benefit of not wasting any starter at all. (I actually keep two starters going; one is a back up in case of disaster!!!)

Andrew