My first 550D shots with 75-300mm lens

Judging by your subject, I would say you're at max focal length (300 mm) and minimum focal distance (about 5 ft) - a quasi-macro shot. Would be interested in the particulars, shutter speed, aperture, ISO, etc.

The EF 75-300 mm is what it is for those of us without deep pockets or passionate interest in long focal lengths. I have the older model without the USM motor or IS. My limitation is not with the lens, but my ability to hold it steady. It wouldn't surprise me if this isn't what is sometimes mistakenly called 'softness.' Outside I keep the shutter speed high and adjust the ISO as necessary. Otherwise, I guess that's what tripods are for. I find my best shots have been inside using the 430 EX flash which has a relatively long zoom reach and further limits the effective shutter speed to the duration of the flash.

Have fun with your new gear.
--
Editor Bob