Beginner roller skating
A Straight Eagle Is a Hip Problem, Not a Skating One
Your spread eagle curves. Everybody's does, and the curved version is the normal one. Holding a dead straight line is a different question entirely: it needs external rotation at the hips that not every body has, and it is not something skating practice will hand you. It is trained off your skates like any other range of motion. Stop rebuilding your technique to fix something your hips are doing. Quad technique, from Najete Kada.
Your spread eagle curves. So does everybody else's, and the curved version is the real thing rather than a lesser version of it.
Holding one in a dead straight line is a separate question altogether, and it is worth being blunt about why. It asks for external rotation at the hips that not every body has, and no amount of skating practice will hand it to you.
That matters because of what people do when a move will not come. They assume the technique is wrong and start pulling it apart, session after session, looking for the cue they missed. There is no cue. It is a range of motion, and a range of motion is trained off your skates like any other.
So do the two things separately. Skate the curved eagle, which is available to you today and is a perfectly good position. Work your hip rotation on the floor at home, on its own schedule. Quad technique, from Najete Kada's Tuto roller series. She is a French champion in artistic roller skating and teaches quad; nothing on this page is a claim about inline skates.
Keep going: this is one section of the full Roller Skating for Beginners guide — sizing, gear, stopping, and where to skate, in one page.