I don't think you need to move the light closer... 3 inches is pretty close!! I have a basic check list when it comes to growth issues, maybe this will assist you in your issue (if it's an issue in the first place but it does not hurt to double check your processes)
1. Over watering will slowly suffocate your roots, preventing sufficient oxygen uptake by the roots, and ultimately causing root rot.
2. Light deprivationAlthough your plant may be receiving light, particular strains may require higher light levels than others. A recommended light level for full bud development is 50 watts/m2. Full sunlight is 100,000 lumens max.
3. Low nutrient Strength The plant is unable to acquire the necessary amounts of nutrients to sustain high growth rates. Large and mature plants can take higher nutrient strengths. Plants under fluorescent lights usually require a lower nutrient concentration than under HIDs.
4. Nutrient Lock Up - Adding too much of a nutrient (ex. Magnesium) can �lockup� one or more nutrients, rendering them chemically unavailable to the plant. Nutrient lockup can occur at extreme pH ranges (ie. under 5.0, over 7.0)
5. Check your PH levels - make sure ph level is ideal to facilitate growth
6. Check temperature of the environment - make sure temp and humidity are ideal
After you check these few simple steps.....monitor and have patience.
Good Luck