Getting out on longboard

I've only started surfing few months ago on 1-2 feet summer waves. The waves are now getting bigger and went up to 6-7 feet over the weekend. I usually get out on smaller waves by doing pushup or I wait until there is a break and paddle out quickly.
This weekend I nearly killed other surfers, I lost the board so many times as I was trying to paddle out and pass the big waves. I turtle rolled and try and pull the nose down as hard as I can but the board didn't go down, instead the wave lifted the board back up and I did a flip. I couldn't hold the board so I tried to grab the leash as there are probably people behind me. It pulled me so hard that I had bruises where the leash is attached. I'm pretty sure I would've lost a few fingers if it got tangled with my hands.
One time when I turtle roll, it flipped my board back up again. I landed on a shortboarder doing duck dive. He was pinned right under my board and our leash got tangled. Luckily he is wearing wetsuit or he probably need stitches.
The board I'm using is southpoint bonga mk2. I'm only 63kg and I tried doing turtle roll on calm water and I still can't even get the nose down. I tried shooting myself forward and put all the weight down in the nose but as soon as the wave pass the tail the nose comes straight back up.
I wasn't the only longboard struggling to get out. The more experienced ones seems to have incredible paddle strength so they paddle out very fast when the wave . There were a few just can't get out at all and they eventually gave up.
I asked the surfer around me for advice, they said you have to turtle roll. If you can't then it's either your skills or the board has too much buoyancy. They told me the waves over the weekend are more suitable for shortboard who can duckdive their way out. They suggested that I get a shortboard as the wave is only going to get bigger in the winter.
This weekend I nearly killed other surfers, I lost the board so many times as I was trying to paddle out and pass the big waves. I turtle rolled and try and pull the nose down as hard as I can but the board didn't go down, instead the wave lifted the board back up and I did a flip. I couldn't hold the board so I tried to grab the leash as there are probably people behind me. It pulled me so hard that I had bruises where the leash is attached. I'm pretty sure I would've lost a few fingers if it got tangled with my hands.
One time when I turtle roll, it flipped my board back up again. I landed on a shortboarder doing duck dive. He was pinned right under my board and our leash got tangled. Luckily he is wearing wetsuit or he probably need stitches.
The board I'm using is southpoint bonga mk2. I'm only 63kg and I tried doing turtle roll on calm water and I still can't even get the nose down. I tried shooting myself forward and put all the weight down in the nose but as soon as the wave pass the tail the nose comes straight back up.
I wasn't the only longboard struggling to get out. The more experienced ones seems to have incredible paddle strength so they paddle out very fast when the wave . There were a few just can't get out at all and they eventually gave up.
I asked the surfer around me for advice, they said you have to turtle roll. If you can't then it's either your skills or the board has too much buoyancy. They told me the waves over the weekend are more suitable for shortboard who can duckdive their way out. They suggested that I get a shortboard as the wave is only going to get bigger in the winter.