either you’re pulling more with your arms therefore targeting the secondary muscle which is your biceps, or you’re gripping the bar too close about shoulder width, use little weight or maybe pullin the bar to almost below your breast. To maintain proper form, you wanna sit with your back straight, chest out and shoulders down. Maintain a slight lean back, and as you pull the bar down, focus on squeezing your shoulder blades together. 💪🏿