Gel Electrophoresis - loading dye and more
The loading buffer you add to your samples for gel electrophoresis has a few different purposes, but the exact amount does not really matter. The purpose of the loading buffer is


to make the sample heavier so it is easy to get into the pocket and stays there
to visualize how far the gel has run
to denature the sample (only for denaturing gels)


Sample buffers for agarose gels usually use something heavier than water like glycerol or sucrose together with a tiny amount of a dye like bromophenol blue. 

So in general there is no issue with using too much dye, but using not enough could lead to the sample being not heavy enough and problematic to pipet, or the sample not being properly denatured. I'd either use 1 ul of the sample buffer (smaller amounts can be annoying to pipett) for your sample, or dilute the sample to 5-10 ul and use the regular amount.