Is my prayer valid if I forget a supplication or a remembrance within it, and it is my intention that if I were to ask a sheikh and he said it was invalid, I would repeat it; does this intention count as interrupting the prayer?

This is not an intention to interrupt the prayer, for you did not intend to interrupt it, nor did you hesitate in interrupting it. Rather, you resolved that if you learned of its invalidity, you would repeat it. There is no evidence for the invalidity of the prayer due to this, and therefore, your prayer is valid.