We are often advised to live in the present moment and not think about the lapsed past and the yet to come future. At any one moment in time, there are overlapping circles of the past, the present and the anticipated future. The past cannot be changed, but lessons can be learnt and a better present and future could result. Dwelling on regrets and remorse is unproductive. Wishing things went differently is “wishful” thinking.
There is another aspect of recollecting the past that could be of benefit. The past has not only bad memories but many good ones. Reflecting selectively on the pleasant ones will bring a smile to your face, and is free of charge! You can indulge in playback of happy events in visual, auditory forms with associated emotions which give you enjoyment.
Thinking of the future is essential for safe and meaningful living. It often requires good decisions based on past experience and present conditions. What is not productive is to speculate on every possibility leading to paralysis of decision making and bad outcomes.
By all means accept that the present moment is the only one accessible now but it does not follow that reflecting on the past and on the anticipatory future is worthless - it is quite the opposite, it helps to make best use of the current moment.