Parent of an only child here too, but on the other side (D graduated college in '93)…
As long as your child has a true safety school on their list that is both affordable and that they love, the college acceptance part shouldn’t be stressful. Extra bonus points if the school has rolling admission so they have an early acceptance.
If your child has ownership over their list and you let them be the driver of the process, that will help them feel more in control. (And IMO, that leads to contentment in the college choice).
Find something new to get involved with in the Fall that you can look forward to for yourself. An activity you’ve back burnered because of parenting responsibilities would be perfect! Maybe even a little vacation after drop off.
Brace yourself now for the teary calls home. Roommate problems, bad grade, homesickness, heartbreak, etc… are par for the course even for kids who are thrilled to be going to school. Listen, be empathetic, and remind them they have the tools and resilience to get through this. Don’t swoop in to rescue and don’t let them come home for the weekend.
Your child has got this and so do you!