What is the future but a culmination of a long series of nows?
I am not saying looking to the past in regret is bad.
I would, however, say that you should place yourself in the shoes of your future self. Ask yourself what your future self would regret not doing in this very moment.
Regret is fruitless without looking right before you, too. The now is a test, the past is our lessons. Demonstrate your learning.
The lead of the past can be alchemized through the fire of meeting the present head-on, heart first. Regret can fuel the loving flame of positive transformation. Rectify, rectify, rectify.