Should i push out my selection date?

Dude, you have 3 months. That's more than enough time for anyone. You could take a Soldier that scores consistent 180s and in 90 days have them more than ready to be successful at Selection (physically). Ruck, run, general upper body. That's all you need to do. The more you prepare the better you'll do. You have a set date, there's tons of people wanting just that. Don't let your brain talk you out of going - that's what keeps 80% of people from even applying.
The same applies while you're there "Shut up brain, just keep walking."

More than being physically ready, you need to be mentally prepared. Going there with self doubt will most certainly have you hanging it up while you are there. I went to Selection only one month after the idea popped into my head. I was I great shape but had to use that month to find myself. 30 days later I was at Camp Mackall showing them who I was. If you are having doubts save yourself the embarrassment. Or man up and find your heart and go show them who you are. Selection was easy.

Unless you are physically injured and not recovered yet, there is no reason to push it back. Selections are designed to push you past your physical capabilities and reveal who you really are when you are completely tapped out. Everyone says they'll never quit, but when you were physically, mentally, and emotionally exhausted five days ago will you actually push your body when your teammates are relying on you? That's what selections are all about.
For example, I came directly out of Basic, AIT, Airborne, then two weeks of holdover at the 75th before attending RIP. I was in the best shape I could have been at that point in my life. It was still the hardest selection I've ever attended. Conversely, when I went to SFAS I was coming out of 68W AIT. I had barely done any PT for three months because we were in reverse cycle. I had a four year break in service prior to that. When I got to my unit I had to do sick call every other day so I missed all the SFAS prep training. I did two short road marches the month prior and none the year prior. Given the choice, I would have taken six months to prepare physically, but I walked into the SORB office and asked them to send me immediately. That was still a tough selection, and there were people better physically prepared who didn't get selected while I did.
Point being, you're either the kind of person who waits for the world to present you an opportunity to succeed, or you're the kind of person who succeeds because you dare the world to try to stop you.