If you have a coverslip, put one on top, draw out excess liquid from the side of it with a bit of tissue or paper towel, and take another look. When using high magnification, your depth of focus is very narrow, so it will be much easier to find focus on something if you can assure it's directly contacting the glass. You should also be able to vary the amount of light to get a bit better contrast - the fourth image is probably the best of them for illumination.
It does look a little like there is a pointed end and a round end to each cell, but at least from that ID guide, movement would normally be expected. Also, what magnification are you at? Some types are different size, so if you divide your eyepiece field number (a 10x18 eyepiece would have an 18mm field number) by your magnification to get the total field of view of the sample ( a 20x objective and a 10x18 eyepiece gives you a 0.9mm field of view), and you can estimate how long a cell is by trying to find how many end to end would span the full field. Not going to be as accurate as having a micrometer in the shot, but good for a ballpark estimate.