Question
If I was afraid of over fertilizing so I did not use enough fertilizer.  I am using Scott's Summer formula and the package says not to fertilize again for 2 months.  The fertilizer has been on the ground now for a 4 days, can I add more fertilizer.  

Answer
No, you should not add any more fertilizer. In summer, using a light application of fertilizer is more than enough even if used at half strength.

If you are located in the north with cold winters (4 seasons) then you probably grow cool season grass and your lawn should NEVER be fertilized in summer. Ever. Just because a commercial company sells a product they rate as "Summer" does not mean it is good to fertilize a cool season lawn in summer and in fact you do more harm than good. You should not fertilize your lawn in summer and not definitely do not add more fertilizer now. Cool season lawns should be fertilized in late spring, early fall and late fall. Never ever in summer.

Warm season grass which is grown in southern areas, such as southern california, florida, and us south east can handle the heat of summer but go dormant in winter as temperatures fall below 60F. These warm season grasses can be fertilized in summer.