If you're not confident in your ability to do well on the June SAT and it's not a financial hardship, you should cancel the June test date. It sounds like you already know you want to apply to schools that require all of your test scores, and you're planning to do more serious study to prepare for the October SAT. While it's true that schools like seeing improvement from test to test, it's much better to just get the high score the first time around.
The only reason not to cancel your June SAT and just take the October SAT is if you are planning on applying early decision or early action to any school; if so, your October SAT scores may not get to the school in time, leaving your application incomplete. But other than Early Action/Early Decision, there's really no reason to take a test you know you're not going to do well on when you'll have to send those scores to colleges you're applying to.
For a deeper dive into consistency and standardized test-taking, read my answer about retaking the ACT for consistency.