sounds like you're trying to do what the Auto Punch is designed to do. Note the red icon in the transport is where this feature is enabled.
Here is the description in the manual (from page 56):
It is sometimes useful to automate the point at which recording begins and ends. For example, if you wish to record over a specific phrase of a vocal part, but not before or after that phrase, you can automatically begin and end recording at specified points. This process is commonly referred to as “punching in and out,” and the resulting new Audio Event is referred to as the “punch-in.”
In Studio One, punching in/out is achieved with the Auto Punch feature. Follow these steps to engage Auto Punch:
1. Set the Left Locator in the Timeline Ruler of the Arrange view at the position you wish to punch in—that is, where
recording should begin.
2. Set the Right Locator in the Timeline Ruler of the Arrange view at the position you wish to punch out, that is,
where recording should stop.
3. Click on the Auto Punch button in the Transport, or press [I] (the letter ‘i’) on the keyboard.
4. With Tracks record-enabled, begin recording at any point before the Left Locator position.
5. Playback begins and recording automatically activates at the Left Locator position. The Record button in the
Transport turns red, the playback cursor continues to scroll from left to right, and new Events begin recording to
any record-enabled Tracks.
6. Recording automatically stops at the Right Locator position. However, playback continues beyond the Right Locator position until you manually stop it by pressing [Space Bar] on the keyboard or by clicking Stop in the Transport.
If you use the Auto-Punch feature in Studio One to record your punch-ins, or if you punch in manually, the newly recorded audio is automatically crossfaded at its edges with the existing Audio Event, so the transition between the old and new audio is not audible. The crossfade time is very small and not audible; however, you can edit the crossfade manually.