Broken my All on 4. Is there anything I can do so that it won't get worse? (Photo)

Sorry to hear about your broken tooth on your All-On-4 bridge.  From your picture, it looks like you are either in your temporary teeth or your finals (if they are hybrids).  In either event, it looks like the teeth are acrylic with an acrylic base.  I can see what looks like acrylic base behind the tooth that is fractured.  Believe it or not, may people will simply use super glue to stick the broken piece of tooth back on.  Now, I am not recommending that...but that is what many people do.  My biggest fear with that option is that the super glue breaks down with the saliva over time and you could possibly swallow the tooth fragment if it dislodges.  The broken tooth will cause no actual harm to the implants.  The sharp edges of the tooth will certainly be annoying, but will cause no permanent damage other than irritating your tongue and lip.  You could use a small fingernail file to smooth the rough edges until you can get into your dentist office.  A minor inconvenience, yes.  But, easily fixed so nothing to get too worried about.

Breakages of acrylic teeth with All-On-4 can occur in about 15% of cases, and it is often a sign of excessive pressures from function or grinding/clenching. It can be easily repaired, but will likely be a recurring problem.
This issues should be addressed in one of the following ways:
Administration of nuromodulators to reduce the biting pressures. This will cost approximately $600 but will need to be repeated every 4 months;Conversion of the acrylic bridge into a Zirconia bridge. This is the most permanent fix, and should cost no more than around $10,000. The Zirconia is more durable and will las much longer than teh acrylic anyway;Wearing a splint can help, but the effectiveness is limited.

Your teeth are made out of acrylic and are easily repaired. The ideal method would be to remove the prosthesis (lower teeth) and send it to a dental lab for the tooth to be replaced. Depending on the lab, the cost should be a few hundred dollars.
If this is a photo of your final set of teeth and you have a temporary, the temporary teeth can be seated so that you are not without teeth for the 2-3 days usually required to make the repair.