Yes. Everyone has a 100 engagement limit.
Yes, you can increase if you ask. I believe Marketo doesn't like to do this for smaller customers.
However, you need to do these steps
1. Shut down every Engagement you do not need --- Setup>OFF
2. Delete any Engagements where you no longer need it and can safely remove the data.
that should keep you below the 100 limit most of the time.
There should be no reason to use 100 Engagements at most firms. I find that the reason people hit the limit is because they setup dozens of Engagements, thinking that's the only way to Nurture, they put 2 emails in 3 streams and forget about the program. This is NOT the best way to use such a powerful tool.