Doggie bed slipcover

So today I decided to make a slipcover for Eddie's (our dog) bed. We'll see how it goes. I of course never measure anything I try to make, I just kind of eyeball it, which usually ends up in disaster. Like when I tried to sew a cushion for Tad's highchair and it ended up 3 times to small than what I had intended. Maybe this will fit. I'm almost finished with it. I just have to figure out a way to close it up on the end. I thought about buttons but I don't really know how to sew button holes. Guess I should do some research before I try to give it a go on my own... that also usually ends up in disaster.