I am looking for scripture that instructs us that the scripture is its own interpreter.
Am I right that it is not man's duty to interpret the scriptures but to accept it
at face value?
There is no specific scripture that says we are to take Scripture at face value. Yes it is NOT man’s duty to do any private interpretation. It is a common belief by Christians that scripture is to be interpreted by Scripture alone (Sola Scriptura). If we are to hold to the truth that the word of God gives, then a bigger question would be what other source for His word would be more accurate? None that I am aware of. The Bible is the inspired word of God and is needed and useful for teaching all truths;
"All Scripture is given by inspiration of God, and is profitable for doctrine, for reproof, for correction, for instruction in righteousness, that the man of God may be complete, thoroughly equipped for every good work." 2 Tim. 3:16
As far as man interpreting the Bible and taking it at face value, we are to take the Bible literally, however that can only be done after proper consideration of the literary forms used and historical context of the passages, and reference to the original language (when necessary). Just reading it at "face value" without doing those things can be troubling at best and wrong. For example, Luke 14:26 reads;
"If anyone comes to Me and does not hate his father and mother, wife and children, brothers and sisters, yes, and his own life also, he cannot be My disciple." Luke 14:26
Reading this verse at face values implies that Jesus is telling us we need to hate our family before we can be His disciple. This goes entirely against what His main message was, which is to love one another. After referencing the word hate to the original Greek language, we see that it is a word (miseo) that means to have "relative preference for one thing over another" In other words, this verse means to have a love for Jesus above all else, even our families.
Interpreting God’s Word requires most of all, prayer for God to reveal the truth to us through the teachings of the Holy Spirit, then intense study. We do this so that we will obey what it says in 2 timothy;
"Be diligent to present yourself approved to God, a worker who does not need to be ashamed, rightly dividing the word of truth." 2 Tim. 2:15