Your 1994D penny might indeed have an error! Those extra bumps you see on the reverse above the 'O' in 'OF' and between the 'ME' could be die chips, a common minting error that happens when parts of the die break and leave raised marks on the coin. Die chips often increase a coin's value slightly, especially if they’re prominent. Enlarging the picture can help verify this. Let us know if you need help with further identification!