flex watt?

Hi I'm trying to get a tank setup for a Leo. I got some extra 6in flex watt heat tape and was wondering if one strip is enough or if I should run two strips side by side to get the full 1/3 of tank. The tank is a glass 20L. Don't want to wire up one section to find out it's not enough and have to rewire it. Pls let me know your opinion it


Thanks

I think 2 strips would be better :)