whay are my arms the same size?

[Prick L]

okay so i lift 100 pound dumbells 10 reps 4 sets every day twice a day i do straight curls 1 day and then the next 2 days i do hammer curls and continue in this pattern i do this because if i did straight curls with 100 pounds every day my arms would break but when i do the straight curls with my left arm i can only get the weight halfway up cause my left arm is soo weak but my arms are exactly the same size (11inches around) and ive been lifting like this for like 2 weeks now and im 15 if that has anything to do with it and ive been lifting for 4 months i started with 20 pound dumbells and increased the weight by 10 pounds every week i just decided to stop increasing the weight when it got to 100 cause 100 is hard to curl