Hey all, excuse me if this is a silly question but are we expecting to see slippage on backtested data? On a minute resolution EURUSD buy/sell?

I was playing around with Forex and EURUSD and attached is an simple algo that trades at a specified minute and sells the next minute after every day. The backtest shows a 95% loss rate (sad face), but my log would say otherwise... I log the moment before buying and the moment before selling and compare the two to see if they would profit or not. End of algorithm displays my expeced win rate of ~67%

Please let me know what I am missing