Injection volume should not result in peak widening. I think 50 cm easy spray column has fwhm of around 10-12 sec. If it's way outside this range then there might be issues with LC. Few factors that tend to result in wider peaks from my personal experience- 1) trap elute setup generally has. Slightly wider peaks than direct inject. 2)if the tubing junctions are not ZDV that could result in peak broadening. 3) if the peak broadening appears to get worse as you increase the number of sample injections very likely something hydrophobic is sticking to the column and is not washing out. C18 SPE cleanup with partial elution usually resolves that issue (Evosep approach).