At the moment your hamstring it strained and may rupture during a race. If it ruptures thats much worse and may very well result in you never getting a sub-3 hour time. Can you honestly say you wouldnt be tempted to carry on running the race if this happened?
Professional careers have been ended by such things Yes they are still able to run but a weak spot is created that simply cannot take the strain of competition again.
Best to go to a physio see what they say and do it.