Hey just a word of advice, I actually sealed my first tank around 2 months ago, i took the time (2 week total with water test) to scrap all the silicone off, clean the edges with alcohol, lay masking tape down and run the bead and used a tool/finger to smooth it out.
Oh and new silicone can bond to old silicone just as long as you clean the bonding surface of the old silicone throughly with alcohol, also when you cut open the tip of the tube remember to use a small screwdriver or something that you can stick in the break the inside seal because if you go to caulk it your just gonna pop the back seal and end up with a huge mess of silicone, and thats what sound like you did and you then resorted to using your hand.
And last silicone sealing is about quality not quantity so just cause you got a whole glob on there it actually might still leak.
So take the time and do it right you will be glad you did.
