If one looks at the Bible as history, then it is the history of a progressive revelation. Beginning with Abraham, it is the revelation of God to a particular people. We Christians believe that that divine history found its fulfillment in Jesus Christ. The Jews deny this, so you would say that the God of Jesus is not the God of the Jews? To the extent that the Koran does teach us about Abraham and teach us what the Bible does, then it is true.
The Koran was made up, Robby. It teaches us NOTHING about the God of Abraham. The Canon of Scripture was CLOSED.
As to the Jews, no, I would not say the same thing about them. The Jews DID have their Scripture revealed by God. It is the true God. They have rejected the second part of it and have an incomplete God and are lost as a result. But the starting point was the same as true Christianity.
Islam has rejecte4d the God of the Jews and the God of Christianity. They deny the trinity. They deny the deity.They deny the crucifixion. They deny the Resurrection. And they do so having rejected the Old Testament as "corrupted" and so don't even have the same God at the start.
In short, ISLAM made up a god and attached it to our God. The Jews and Christians did not make up a God. He is true God even if the Jews reject certain aspects of Him.
Allah is in NO WAY synonymous with the God of Scripture. They made him up.