Some good, beginner accuracy exercises

[the ancient one]

You need mirror time.

look for and avoid in the lunge:

the leading foot and knee turning in
bending the back either forward or over. keep it straight
dropping the head, twisting the head
twisting the trunk
lifting the shoulder
fully extend the arm but don't lock the joint

you are learning:

isolate accuracy, speed and distance
don't go for the longest possible lunge yet
you can extend the reach over time as accuracy and speed develop
don't go for the maxumum possible speed. work that up gradually too.

close you eyes:

advance/retreat, then open and check your position
lunge with your eyes closed and then open and check
you need "muscle memory" and kinesthetic sense independent of vision.

As others have said above
be careful with "target practice" you can wind up with just the ability to hit at exactly one distance with terrible body position. This won't translate into
successful fencing. I am not saying don't do it, just don't do it without specific feedback on the points above.

good luck.