Weaving with a temple is not for straight selvedges but for keeping the outer warp threads from breaking due to rubbing on the reed caused by draw-in. Some experts recommend that you never weave without one. Using a temple has greatly improved my weaving.
If you don't have a temple or the cash for a fancy one, you can easily improvise one with inexpensive materials.
If your loom doesn't have side supports, attach a curtain rod to the side of your loom. If you don't want to do that, install an eye screw behind the breast beam where it meets the side of the loom and thread your rope/string through the eye screw.
Take a couple of, 1lb bags of dried beans (found at the grocery store) or rice and cover them with cloth. Bend a paper clip to make a hook on the bags. Then tie some string to the "hook". Attach tarp clamps or suspender clips to the other end. You can find tarp clamps in the hardware store in the rope and tarp section. Sturdy suspender clips can be reclaimed off used suspenders from the thrift store. I like the suspender clips the best as I found trying to unlock the tarp clamps hurt my arthritic hands. The suspender clips are easier to work.