First, I'm not aware of any forum feature that will automatically post a reply after some time interval. Maybe there's something about your particular setup that's unintentionally clicking "Post reply". You'll need to provide details like: device (Mac, phone, iPad), OS version, browser (Safari, Firefox, etc.), and the input devices you're using (trackpad, keyboard, mouse, etc.).
Second, there should always be a button below any post you've made that says "Edit". It should be right next to the "Report" button. You can click "Edit" and edit your post. Alternatively, you can click "Report" on any post you've made and ask for it to be deleted.
If you discover you've somehow made two adjacent posts that should be merged, click "Report" and ask us to merge them.
You can test the "Edit" button behavior in this thread. Reply to this post and intentionally click "Post reply" immediately. Confirm the "Edit" button appears, then click it to resume editing.
I've occasionally brushed my palm very lightly against the trackpad of my MacBook Pro and had it register as a tap. If the cursor is positioned over a button, it activated the button. When I'm thinking about what to write, I've learned the habit of lifting my wrists while idle, or completely removing hands from keyboard. The palm-brushes seem to happen more in the winter when the air is dry, or maybe its my skin that's drier.