Too much baking powder? Your baked goods might taste tinny and metallic. Like licking a battery. Not recommended. Too little? Your cake will be a sad, flat pancake.
Double-check your baking powder. Is it still active? Drop a teaspoon in hot water. If it fizzes like a tiny volcano, you’re golden. If it sits there like a boring puddle, buy new baking powder. Now.
How To Make Self-Rising Flour - ~ Texas Homesteader
Pro tip: Don’t make a huge batch of this mix unless you’ll use it in a month. The baking powder can lose its OOMPH. Make it fresh, make it often.