HELP! Question that needs some answers

Hey guys! I have been trading the last 5 days and have made great progress. The only thing is. I just did a sell purchase at 90.77 and i left it for a while and then came back and it auto bought at 90.89 and then resold the damn lot at 90.89. I never gave the order but it has happened before. Did i miss something about this? How is it that this auto sell and buy can occur? What is causing this. and now ill probably have to sell immediately when they forex opens Sunday, to keep from anymore of a loss.