Welcome to the forum Katy.
Yes, the photos from the 50D probably are huge...4752 x 3168 pixels. That is a lot of pixels, considering that a typical monitor resolution might be 1200x1000 give or take.
But if you want to print those photo, you may want/need up to 300 pixels per inch of print. So with your file size, that is just over a 15" print. That's big...but not huge. Not to mention that the image will loose pixels if you crop it etc.
So while the image is huge on a screen, there is a reason it's that big.
In Photoshop, you can change the magnification (zoom) of the display. If you tried to view your images at 100%, they would be much larger than the screen...but if you zoom out to 25%, it might fit just fine.
Now, keep in mind that this doesn't actually change the 'Image size'. You can re-size the image (change the number of pixels) to make it bigger or smaller for your intended use. So if you want to upload your photos for viewing on the web, then you will want to resize them (save a copy) to a size that will fit on people's monitors at 100%.