My pattern calls for 2 different colours of yarn to be used like one however I would rather use just one. Do I have to adjust the pattern in any way? is this even possible? here is the pattern I’m using:

Please suggest anything that comes to mind!

No you can use just one color, but you need 2 strands of yarn anyway, or a really thick yarn. Though if you use just one strand and a size 10½ needle, it could work okay too. If you want something the same size, you’d need about 18 or 20 sts instead of 14.