As you have the power-voltage curve, finding the maximum power point is easy: it's the turning point on the power-voltage curve.
The problem is that the absolute values in your graph look completely wrong. If the graph is flipped upside down, and based at zero power, zero current and zero voltage, then the blue curve does indeed look like an I-V curve for a photovoltaic cell, and the orange curve looks like the corresponding power curve.
So it looks like the shape of your curve is right (albeit upside down from the usual presentation), but the absolute values are wrong.
You need to work out what the right absolute numbers are.
You know that the lowest the actual voltage is going to be is zero, and the lowest observed value is currently marked as -10V. The curve is the right shape going left to right (it's upside down, but does not also need reflecting in a vertical axis), so the correction coefficient for voltage is going to be positive. You know that the lowest the actual current and the actual power can be is also zero, and their lowest observed values are marked as 0.1A and about 6.9W respectively - I say lowest, because we need to flip the curve upside down. And because we do, you know the coefficient to correct them will be negative. And you know that $P_{real}=I_{real}V_{real}$.
Given the shape of the curves, it's safe to assume that current and voltage each need a linear transformation (i.e. $V_{real} = aV_{obs}+b$, where you need to find $a$ and $b$)
This gives you a set of simultaneous equations you can solve, to transform observed voltage (current/power) [$V_{obs}, I_{obs}, P_{obs}$] into actual voltage (current/power) [$V_{real}, I_{real}, P_{real}$].
Write out those simultaneous equations, and solve them.
That's the recipe on how to solve it. You'll need to follow the recipe yourself, though: given that this is coursework, there's no use in me doing it for you. Be sure to go through the recipe yourself, and make sure you understand why each step exists - try to work out how I derived it.
