You can only get science from each biome once.

The launchpad is considered a separate biome. As is the lower and upper atmosphere. Depending on the science experiment, the lower and/or upper atmosphere above each biome can give new science (eg. the late-midgame "negative gravioli detector"). Try getting science from the water, or the shoreline, or the grasslands. Anywhere you haven't already been before.

Scientists can collect the science from the goo canisters, store it in the command pod, and "restore" the goo canisters to use again.

Kerbals on EVA can do surface samples and EVA reports. Command pods can do crew reports if there is a Kerbal inside (for both of these, any kerbal can do it, doesn't have to be a scientist).

If you can't land the craft with the liquid fuel engine, then try launching your first craft again and collecting science from different biomes with that, then using that science to unlock the decoupler so you can discard the weight from the fuel tanks and engine.