In any new position, you will have to learn and grow into it and if the jump is gradual, all the better. Assuming that you have the engineering domain covered, you may only lack experience on the management side which will have to be worked on but that will be easier since it is a small company and hence will not be onerous. You can also request help (i.e. informal mentoring from peers/seniors) and later on grow your team to delegate some burden off of you if needed. Necessary commitment and hard-work will take you up the career ladder.

Finally, don't sell yourself short while also not losing sight of your limitations. Focus and sell on your strengths while simultaneously working on improving your weaknesses i.e. stretch yourself and don't always stay within your "comfort zone". Have a clear view of Expectations vs. Responsibilities and you can takeup any challenge.

Good Luck!