Can I travel to Greece using my French Schengen visa? I went to France for 4 days but I really want to go to Greece for 10 days I suppose I can visit France a few more times to make up the days to 10. I'm worried, however, that there will be problems at the Greek border.
You mentioned in comments that the visa you have is a 1-year multiple entry visa, and that you have already completed the trip to France you originally applied for.
In that case, you should have no problems at all. With a multiple-entry visa, after it has has been used for the trip that it was originally issued for, it is valid for subsequent trips to anywhere in the Schengen area without further ado.
The reason why getting a visa from one Schengen country and using it for a different one can be problematic is that it raises an inference that you were lying to the issuing country when you said you were planning a trip with it as a main destination. But in your case, then you did complete the trip to France as planned, there is no issue of telling them something that turned out not to be true.
Yes, you can travel to Greece using the French Schengen visa. Actually I travel the same route last year. First I arrived Paris for 2 days, then went to Rome for 3 days... the last station is Athens and Santorini. According Schengen Agreement, I must spend the longest time in French, but it seems no border officers care about that, so I didn't have any problems entering and leaving the Greek border.