A pdf version of the book "Problems in Mathematical Analysis" written by Demidovich, a famous Belarus mathematician. It's a long exercise so I recommend doing only the odd/even number questions.
I've finished my calculus class, and this book did help me a lot. I didn't finish all the questions but only focused on those related to limits and integrals. Some of the questions are highly similar, while some are quite inspirational and creative (e.g., using the Euler formula to calculate certain integrals with trigonometric functions). If you're not confident with doing engineering maths without practice, this book is a must-have. (It's likely not for pure mathematics because of the high similarity across questions and lack of advanced content of real analysis. Take it with a grain of salt since I'm not a math major.)