1) It's chipped along the silicone. If part of the glass touching the silicone came loose I would get a new tank
2) It is at the lowest point on the tank and will have 100% of the water pressure pushing on it all the time. This would concern me in the long run, not necessarily right now, but 6 months from now when you think everything is fine, the seam may let go.
Only being 65g, I would go get another one. It sucks, but peace of mind is what you need.
I had a 190g tank with a chip half way up one corner for 3yrs. EVERY TIME I looked at the tank I thought about the chip and what could happen.