it doesn't matter how many megapixels your camera has, the best quality lenses for 35mm format will gas out at about 16X20 size. good 35mm lenses will be noticably blurry at this magnification. try printing some samples of your photos on 8X10 paper, ...
Any decent printer should deliver what you give them to print, obviously. The problem is this: digital files are never recorded in a dimensional format that EXACTLY fits any conventional print size. Most digital camera sensors are CLOSE to the ratio ...
If you go to a one hour photo "lab" you can ask them for negatives only, but I don't know if they can do that. The machines are pretty much automated, so you may have to get your 4X6 prints. You can go to a camera store that uses a regular photograph...