I hope you not using JMeter in GUI mode. If you do - please switch to command-line non-GUI mode as JMeter GUI is very resource intensive and may ruin your test.
The same for the Listeners: if you have View Results Tree or View Results in Table listeners added and enabled - remove or disable them as they consume a lot of CPU and RAM.
Follow recommendations from JMeter Performance and Tuning Tips guide - this way you will be able to simulate much more than 100 virtual users.
Another piece of advice: if you going to do some testing on REST API - it's likely that you'll have to deal with JSON data. Vanilla JMeter's JSON support is not so good so I recommend using the following test elements:
Both are available via "Extras with Libs" set of the JMeter Plugins project.