Sources of Error in Youngs double slit experiment

Welcome to PF;
Well... what kinds of error are there?
What sort of thing gives rise to each kind?

 

There are systematic and statistical errors - besides downright mistakes, which your teacher is calling "human error".
Ignoring mistakes ... systematic and statistical errors come in every time you measure something, or use a value that someone else has measured.
So list everything you have measured and pay attention to how you measured it.
How inaccurate was the measurement (statistical error), and was there anything about the method that could have given a consistently high r low reading (systematic error)?

 

Consider a possible purpose of experimentation: to understand a seemingly cold and detached equation; you are understanding how the experiment yielded the equation: conversely, how might a variance between equation and experiment signify you have made a mistake?

From this perspective, notice how the variables in your equations:

dsin(Θ) = mλ
dsin(Θ)= (m + 1/2)λ ​

May have influenced your results; for example: was the order of interference you observed counter to what it should have been? (m as dependent upon the ratio of the product of distance between slits and the color of laser used). In this scenario, one error could have been that you spaced the slits too far apart, so d was too great.