Your order may have been squared off before 3:20 PM due to one of the following reasons:
1. Insufficient Margin: If your account did not have sufficient margin to maintain the position, it could be automatically squared off by the system to prevent losses.
2. Risk Management: If a stock is highly volatile, Groww may square off intraday positions to avoid circuit limits (no buyers/sellers). For example, if the price moves beyond 16% from the previous day's close, Groww may square off short positions if the price rises by 16%, and long positions if it drops by 16% to prevent auction and circuit risks.
Details of the same are mentioned in the policy and procedures as well. You can refer to them