The party was of the workers and had open elections among the workers. Opposition parties were banned, but that does not mean it wasn't open.
The Party was absolutely not Bourgeoisie. The fact that workers owned the state and the party ran the state does not mean that the Party were bourgeois. This is a ridiculous notion, akin to saying middle-management in a Capitalist enterprise are bourgeoisie because they run much of Capitalist companies.
The party had the same class interests because there was no M-C-M' circuit by which state planners pocketed all of the profits. Production was directed by the state and flowed back to the workers in the form of free education, health care, pensions, and other worker-directed benefits. It was not used among competing Capitalists to gain monopoly and increase exploitation.
You should reread Marx, your understanding of class dynamics is highly flawed.