I would encourage you to stop over-thinking. If you believe in the oneness of our creator and associate no partners with HIM and believe our prophet Muhammad s.a.w is the last and final prophet then please accept and take your shahada. Best to visit your local masjid if you able to and take your shahada there but if not you can take it at home.
Please watch this very quick video of how to take the shahada.
Please let us know how you get on. You might find this show interesting and informative to watch insha Allah
If you need anything please let us know.
May Allah swt make things easy for you Ameen.