Is Israel expanding?

Yes. The UN has told it to go back to its 1967 borders.

To be precise, the UN has said no such thing, and there aren't any borders from before 1967, only ceasefire lines the 1948 War of [Israel's] Independence where the agreement stated that such lines have no political or legal significance and do not prejudice future negotiations on boundaries.

But to address the question, the size of Israel has grown and shrunk over last 100 years.

To begin with, the area known as Palestine stretched from the Mediterranean to the borders of Mesopotamia (now Iraq). The League of Nations (the fore-runner to the UN) designated Palestine as a National Homeland for Jews.

SHRUNK: The British was given responsibility for Palestine (their Mandate) and promptly gifted half of it to the Emir Abdullah, then known as Trans-Jordan.

SHRUNK: UN resolution proposed a partition plan for the remaining half between Jews and Arabs, which the Arabs inside the British Mandate of Palestine and outside rejected. The Palestinian Jews declared Independence within the proposed partition, and the Arab armies attacked, and lost.

GREW: Legally, it is unlawful to acquire territory by conquest, but an exception is made when territory is captured during a defensive war (see precedents of Sudetenland and Koenisberg).

SHRUNK: Gaza was illegally annexed by Egypt, and Judea and Sumaria by Jordan.

GREW: In 1967, Egypt and surrounding Arab armies massed on the 1948 ceasfire lines and threatened to annihilate Israel. Israel launched an pre-emptive attack against Egypts airforce and Jordan and Syria joined in the fighting. Syria lost the Golan heights, Jordan the West Bank and Egypt the Sinia and Gaza.

SHRUNK: Israel gave Sinia back in echange for peace with Egypt. Egypt didn't want Gaza, but that was withdrawn from voluntarily in 2005.