I would trust my own results over those from a pool store.

If your FC is >10, that is pretty vague. It could mean 11 or it could mean 30 or ?? So, without having a more accurate reading, it is hard to know what your FC reading will be by Saturday. If your test kit won't read high enough for the amount of chlorine in the water, you can dilute your sample. Take one part pool water and one part distilled water, test as usual and then multiply the result by 2. If that doesn't take it high enough, take one part pool water and 2 parts distilled, then multiply by 3, etc. You do lose some accuracy the more you dilute, but it will give you a better reading than just "greater than 10."