Allergy eye drop overdose?

I used some eye drops (2 drops per eye) for my itchy eyes abut maybe 3 hours ago. Then just about 10 minutes ago they started to itch real bad so I put in one more in each eye. Do you think thats fine? Its not an overdose is it? It says use no more than 4 does a day and that would be every 6 hours, but I took a second dose at 3 hours. Will this harm my eyes?