Adjusting grain bill for my system

Northern brewer doesn't offer grains in ounces, so you have to buy a whole lb. I'm making the NB cream ale kit. Their kits are set on 75% efficiency, but I've been getting only 70% (only made a couple all grain batches). I plan on going from 1.25 qts/ lb to 1.5. Should this make up the 5%? I ordered an extra lb of the 2-row, but didn't order any more biscuit/honey malt b/c I would have wound up wasting a good bit of the extra lb I would have bought since I don't have a mill and have to buy pre crushed. If I just add the extra 2-rows to bump up the gravity without extra specialty malt, will this throw things off too much?

If you're batch sparging then I would put the extra water in the sparge and not the mash. I batch sparge and let it set in my mash tun for about 10 minutes before collecting the liquid. I always overshoot the sparge water amount and I've been hitting around 78% as of late. The increased boil time isn't great but it works out well.

What you need to do if you want to be exact is figure out how many gravity points the 5% is. Then figure out how much grain you need by using the extract potential of the grain. An easy way to this would be to plug the recipe into some software, set the efficiency @ 70%, play with base malt amount until you hit your desired OG. You could also go the route of making a slightly smaller batch. Or just chuck in the extra pound and RDWHAHB.

Well I have plugged it into software, and have it pretty close. My main thing is I'm just worried by adding extra base malt and not adding extra specialty grain, I'm going to alter the taste of the beer. Am I the only one who feels like I have to have at least 5 gallons. It's a huge bummer when I get less than 48 bottles out of a batch. haha I need to get over it, but the joy of having 50+ is so nice!

From what I understand adjusting just the base malt for efficiency is what you want to do. You'll be fine.