Casual self-evaluation with self-deprecating humor. ボク in katakana is a stylized, childish-or-youthful masculine first-person. 今じゃ is casual for 今では. 100点中 ('out of 100 points') uses 中 for 'out of, within.' 赤点 ('red mark, failing grade') refers to the red marks teachers use for failing grades — traditionally below 60 in Japan. The speaker is proud of being above failing (even though 45 is objectively low).