Physics Poster Practical Help!

[WTFBBQCheesecake]

Hi guys,
So I was doing my physics poster on the loss of energy in a spring system. I initially had a spring hang freely off of a clamp (Calculated it's k value beforehand), measured its length, added a 50 g mass to it and waited till it was in equilibrium. I then lifted the mass up 10 cm and dropped it, measuring the distance of the lowest point of oscillation. Now the problem is, when I calculate the initial energy minus the final energy (to see if energy is lost or gained), I found that the change was a negative value. This would mean that the spring gained more energy then it had to begin with but I can't find a good reason as to why. My teacher said that this was a real phenomena and that I need to think more deeply about it. I can't see any other reason besides the fact that it was an open system.

Can anyone help answer why this is occurring?

Thanks for your help

[Srd2000]

Hey, shouldn't you be using the final energy minus the initial energy? Because thinking of from an energy view, if you final was 10J and initial was 15J then the change in energy is 10-15=-5 meaning that 5J was lost because it was a negative value.
Are you dropping the mass from a higher height each time?

[WTFBBQCheesecake]

Hey, shouldn't you be using the final energy minus the initial energy? Because thinking of from an energy view, if you final was 10J and initial was 15J then the change in energy is 10-15=-5 meaning that 5J was lost because it was a negative value.
Are you dropping the mass from a higher height each time?

Yes we are. However, we chose initial-final because we wanted to see what the change was from the initial drop height (when i was holding the mass/spring) to the final energy state which we defined as the lowest point of oscillation. It shouldn't matter which way you do it, as long as you define what positive and negative mean. We saw that the intial energy was less (e.g. 1 J) and final energy was more (e.g. 1.5 J) and so there was a gain in energy. I just can't figure out where this extra energy could come from :/

[Srd2000]

Not sure I understand your method, but what I could suggest as a solution could be from the gravitational potential energy it gains, discrepancies in the elastic band or simply magic. If you send me a clear method or a diagram of how you set it up I can provide a more accurate answer.