Congratulations on your first Groove, Dimitar! And it's in Bulgaria! Time to celebrate!
It appears you used the large bit on this one, Dmitar. If not, then you still did right. Sometimes the best we can do is all that we can do...
Still, this can be easily repaired. Simply fill in the entire groove with metal epoxy of your choice, sand the secondary wall down smooth and use the next smaller bit.
While the small bit used in an automobile-sized engine will show minimal gains, ANY gain is a good one!
Don't lose faith, my friend and remember you have to work awfully hard to screw this up.
So, fill 'er in and roll on.
Sometimes that's all we CAN do.