Need advice

I am a software engineer with 3 years of experience .For the first two initial years I was working as a QA in one of the good product companies with a very sorted work life balance . I had recently switched to a BE role in a startup I am very much lagging behind here because of my QA background ,the people here are very much talented and are great problem solvers .How do I reach that level ? I have been struggling to keep up with the pace here and finding it difficult to approach the tasks,even though i have been giving so much of time to work . And the TL in my team have a certain amount of expectations and hence they don't help according to that .(which i feel is fair) How should I approach this and level up here Anyone with a similar background and story please share your experience :) Any advice would really help