Thats no good ,friend.
You dont want the LED to get near those temperatures. Even though the roof sealant will survive, it has no thermal conductivity. The heat HAS to get from the LED to the heatsink.
The roof sealant is acting as a blanket, holding the heat in.
No good.
When you find a larger heat sink, drill 2 holes and use screws to hold it down. Self-tapping screws work great for this, and can be found everywhere.
Your heat sink is MUCH TOO small.
If that were a solid chunk of aluminum, it would work better, OR add a fan.