Once the bell rings (or whatever signal your ring is using) you have 45 seconds to enter. That is a pretty long time. Don't hear the ring and turn so sharply that you squeal rubber to rush into the ring. This will get you AND your horse too tense. Make a nice large slow turn, swing nice and wide so that you have a straight entry into the ring. As soon as the bell rings, take several deep breaths and make yourself relax.
If you are at a show with several rings side by side, Make sure you know what signaling device YOUR ring is using. Each ring will have a different device. It is up to YOU to know what your ring is using. It is not uncommon for a rider to make a mistake and enter their ring on another rings bell. A bad way to get eliminated.
Have a great time and PLEASE post a video of your ride. I would love to see a western dressage ride!!